Astronomy Picture of the Day Search Results for "Star Formation"

APOD: 2009 March 5 - IC 5146: The Cocoon Nebula
Explanation: Inside the Cocoon Nebula is a newly developing cluster of stars. Cataloged as IC 5146, the beautiful nebula is nearly 15 light-years wide, located some 4,000 light years away toward the northern constellation Cygnus. Like other star forming regions, it stands out in red, glowing, hydrogen gas excited by young, hot stars and blue, dust-reflected starlight at the edge of an otherwise invisible molecular cloud. In fact, the bright star near the center of this nebula is likely only a few hundred thousand years old, powering the nebular glow as it clears out a cavity in the molecular cloud's star forming dust and gas. This exceptionally deep color view of the Cocoon Nebula traces tantalizing features within and surrounding the dusty stellar nursery.

APOD: 2009 February 20 - Snake in the Dark
Explanation: Dark nebulae snake across a gorgeous expanse of stars in this telescopic view toward the pronounceable constellation Ophiuchus and the center of our Milky Way Galaxy. In fact, the twisting central shape seen here is well known as the Snake Nebula. It is also listed as Barnard 72 (B72), one of 182 dark markings of the sky cataloged in the early 20th century by astronomer E. E. Barnard. Unlike bright emission nebulae and star clusters, Barnard's nebulae are interstellar dark clouds of obscuring gas and dust. Their shapes are visible in cosmic silhouette because they lie in the foreground along the line of sight to rich star fields and glowing stellar nurseries near the plane of our Galaxy. Many of Barnard's dark nebulae are themselves likely sites of future star formation. Barnard 72 is about 650 light years away. With bluish star 44 Ophiuchi at bottom left, the intriguing star field spans nearly 2 degrees or almost 20 light-years at the estimated distance of the Snake Nebula.

APOD: 2009 February 5 - NGC 604: X-rays from a Giant Stellar Nursery
Explanation: Some 3 million light-years distant in nearby spiral galaxy M33, giant stellar nursery NGC 604 is about 1,300 light-years across, or nearly 100 times the size of the Orion Nebula. In fact, among the star forming regions within the Local Group of galaxies, NGC 604 is second in size only to 30 Doradus, also known as the Tarantula Nebula in the Large Magellanic Cloud. This space-age color composite of X-ray data (in blue hues) from the Chandra Observatory, and Hubble optical data shows that NGC 604's cavernous bubbles and cavities are filled with a hot, tenuous, X-ray emitting gas. Intriguingly, NGC 604 itself is divided by a wall of relatively cool gas. On the western (right) side of the nebula, measurements indicate that material is likely heated to X-ray temperatures by the energetic winds from a cluster of about 200 young, massive stars. On the eastern side the X-ray filled cavities seem to be older, suggesting supernova explosions from the end of massive star evolution contribute to their formation.

APOD: 2009 January 17 - IC 410 and NGC 1893
Explanation: Dusty emission nebula IC 410 lies about 12,000 light-years away in the northern constellation Auriga. The cloud of glowing gas is over 100 light-years across, sculpted by stellar winds and radiation from embedded open star cluster NGC 1893. Formed in the interstellar cloud a mere 4 million years ago, bright cluster stars are seen just below the prominent dark dust cloud near picture center. Notable near the 7 o'clock position are two relatively dense streamers of material trailing away from the nebula's central regions. Potentially sites of ongoing star formation, these cosmic tadpole shapes are about 10 light-years long. Emission from sulfur atoms is shown in red, hydrogen atoms in green, and oxygen in blue hues in this false-color, narrow band composite image.

APOD: 2008 December 29 - NGC 1569: Starburst in a Dwarf Irregular Galaxy
Explanation: Grand spiral galaxies often seem to get all the glory, flaunting their young, bright, blue star clusters in beautiful, symmetric spiral arms. But small, irregular galaxies form stars too. In fact, as pictured here, dwarf galaxy NGC 1569 is apparently undergoing a burst of star forming activity, thought to have begun over 25 million years ago. The resulting turbulent environment is fed by supernova explosions as the cosmic detonations spew out material and trigger further star formation. Two massive star clusters - youthful counterparts to globular star clusters in our own spiral Milky Way galaxy - are seen left of center in the gorgeous Hubble Space Telescope image. The above picture spans about 8,000 light-years across NGC 1569. A mere 11 million light-years distant, this relatively close starburst galaxy offers astronomers an excellent opportunity to study stellar populations in rapidly evolving galaxies. NGC 1569 lies in the long-necked constellation Camelopardalis.

APOD: 2008 December 26 - The Elephant's Trunk in IC 1396
Explanation: Like an illustration in a galactic Just So Story, the Elephant's Trunk Nebula winds through the emission nebula and young star cluster complex IC 1396, in the high and far off constellation of Cepheus. Of course, this cosmic elephant's trunk is over 20 light-years long. This false-color composite was recorded through narrow band filters that transmit the light from hydrogen (in green), sulfur (in red), and oxygen (in blue) atoms in the region. The resulting image highlights the bright swept-back ridges that outline pockets of cool interstellar dust and gas. Such embedded, dark, tendril-shaped clouds contain the raw material for star formation and hide protostars within the obscuring cosmic dust. Nearly 3,000 light-years distant, the relatively faint IC 1396 complex covers a large region on the sky, spanning over 5 degrees. This dramatic close-up covers a 2 degree wide field, about the size of 4 Full Moons.

APOD: 2008 December 10 - Portrait of NGC 281
Explanation: Look through the cosmic cloud cataloged as NGC 281 and it's almost easy to miss stars of open cluster IC 1590. But, formed within the nebula, that cluster's young, massive stars ultimately power the pervasive nebular glow. The eye-catching shapes looming in this colorful portrait of NGC 281 are sculpted columns and dense dust globules seen in silhouette, eroded by intense, energetic winds and radiation from the hot cluster stars. If they survive long enough, the dusty structures could also be sites of future star formation. Sometimes called the Pacman Nebula because of its overall shape in wider-field views, NGC 281 is about 10,000 light-years away in the constellation Cassiopeia. This composite image was made through narrow-band filters and shows emission from the nebula's hydrogen, sulfur, and oxygen atoms in green, red, and blue hues. It spans over 80 light-years at the estimated distance of NGC 281.

APOD: 2008 November 28 - Probably a Planet for Beta Pic
Explanation: A mere 50 light-years away, young star Beta Pictoris became one of the most important stars in the sky in the early 1980s. Satellite and ground-based telescopic observations revealed the presence of a surrounding outer, dusty, debris disk and an inner clear zone about the size of our solar system -- strong evidence for the formation of planets. Now, infrared observations from European Southern Observatory telescopes incorporated in this composite offer a detection of a source in the clear zone that is most likely a giant planet orbiting Beta Pic. Designated Beta Pictoris b, the new source is more than 1,000 times fainter than the direct starlight that has been carefully subtracted from the image data. It is aligned with the disk at a projected distance that would place it near the orbit of Saturn if found in our solar system. Confirmation that the new source is a planet will come if future observations can demonstrate that the source moves in an orbit around the star. When confirmed, it will be the closest planet to its parent star directly imaged ... so far.

APOD: 2008 November 11 - The Cosmic Web of the Tarantula Nebula
Explanation: First cataloged as a star, 30 Doradus is actually an immense star forming region in nearby galaxy The Large Magellanic Cloud. The region's spidery appearance is responsible for its popular name, the Tarantula nebula, except that this tarantula is about 1,000 light-years across, and 180,000 light-years away in the southern constellation Dorado. If the Tarantula nebula were at the distance of the Orion Nebula (1,500 light-years), the nearest stellar nursery to Earth, it would appear to cover about 30 degrees (60 full moons) on the sky. The spindly arms of the Tarantula nebula surround NGC 2070, a star cluster that contains some of the brightest, most massive stars known. Intriguing details of the nebula are visible in this scientifically-colored image. The cosmic Tarantula also lies near the site of the closest recent supernova.

APOD: 2008 October 30 - Haunting the Cepheus Flare
Explanation: Spooky shapes seem to haunt this starry expanse, drifting through the night in the royal constellation Cepheus. Of course, the shapes are cosmic dust clouds faintly visible in dimly reflected starlight. Far from your own neighborhood on planet Earth, they lurk at the edge of the Cepheus Flare molecular cloud complex some 1,200 light-years away. Over 2 light-years across and brighter than the other ghostly apparitions, the nebula known as Sh2-136 near the center of the field is even seen in infrared light. Also cataloged as Bok globule CB230, the core of that cloud is collapsing and is likely a binary star system in the early stages of formation.

APOD: 2008 October 26 - Massive Stars in Open Cluster Pismis 24
Explanation: How massive can a normal star be? Estimates made from distance, brightness and standard solar models had given one star in the open cluster Pismis 24 over 200 times the mass of our Sun, making it a record holder. This star is the brightest object located just above the gas front in the above image. Close inspection of images taken recently with the Hubble Space Telescope, however, have shown that Pismis 24-1 derives its brilliant luminosity not from a single star but from three at least. Component stars would still remain near 100 solar masses, making them among the more massive stars currently on record. Toward the bottom of the image, stars are still forming in the associated emission nebula NGC 6357, including several that appear to be breaking out and illuminating a spectacular cocoon.

APOD: 2008 October 25 - NGC 602 and Beyond
Explanation: Near the outskirts of the Small Magellanic Cloud, a satellite galaxy some 200 thousand light-years distant, lies 5 million year young star cluster NGC 602. Surrounded by natal gas and dust, NGC 602 is featured in this stunning Hubble image of the region. Fantastic ridges and swept back shapes strongly suggest that energetic radiation and shock waves from NGC 602's massive young stars have eroded the dusty material and triggered a progression of star formation moving away from the cluster's center. At the estimated distance of the Small Magellanic Cloud, the picture spans about 200 light-years, but a tantalizing assortment of background galaxies are also visible in the sharp Hubble view. The background galaxies are hundreds of millions of light-years or more beyond NGC 602.

APOD: 2008 October 19 - In the Center of the Lagoon Nebula
Explanation: The center of the Lagoon Nebula is a whirlwind of spectacular star formation. Visible on the upper left, at least two long funnel-shaped clouds, each roughly half a light-year long, have been formed by extreme stellar winds and intense energetic starlight. The tremendously bright nearby star, Hershel 36, lights the area. Vast walls of dust hide and redden other hot young stars. As energy from these stars pours into the cool dust and gas, large temperature differences in adjoining regions can be created generating shearing winds which may cause the funnels. This picture, spanning about 5 light years, was taken in 1995 by the orbiting Hubble Space Telescope. The Lagoon Nebula, also known as M8, lies about 5000 light years distant toward the constellation of Sagittarius.

APOD: 2008 October 18 - Sharpless 171
Explanation: Cosmic pillars of cold molecular gas and clouds of dark dust lie within Sharpless 171, a star-forming region some 3,000 light-years away in the royal constellation Cepheus. This tantalizing false-color skyscape spans about 20 light-years across the nebula's bright central region. It also highlights the pervasive glow of emission from atomic gas using narrowband filters and a color palette made popular in Hubble Space Telescope images. Powering the nebular glow are the young, hot stars of a newly formed cluster, Berkeley 59. Of course, this star-forming region is entry number 171 in the famous 1959 catalog of emission nebulae compiled by astronomer Stewart Sharpless.

APOD: 2008 September 28 - Young Stars of NGC 346
Explanation: The massive stars of NGC 346 are short lived, but very energetic. The star cluster is embedded in the largest star forming region in the Small Magellanic Cloud, some 210,000 light-years distant. Their winds and radiation sweep out an interstellar cavern in the gas and dust cloud about 200 light-years across, triggering star formation and sculpting the region's dense inner edge. Cataloged as N66, the star forming region also appears to contain a large population of infant stars. A mere 3 to 5 million years old and not yet burning hydrogen in their cores,the infant stars are strewn about the embedded star cluster. In the above false-color Hubble Space Telescope image, visible and near-infrared light are seen as blue and green, while light from atomic hydrogen emission is red.

APOD: 2008 September 27 - M83: The Thousand Ruby Galaxy
Explanation: Big, bright, and beautiful, spiral galaxy M83 lies a mere twelve million light-years away, near the southeastern tip of the very long constellation Hydra. Prominent spiral arms traced by dark dust lanes and blue star clusters lend this galaxy its popular name of the Southern Pinwheel. But reddish star forming regions that dot the sweeping arms highlighted in this sparkling color composite also suggest another nickname, The Thousand-Ruby Galaxy. About 40,000 light-years across, M83 is a member of a group of galaxies that includes active galaxy Centaurus A. The core of M83 itself is bright at x-ray energies, showing a high concentration of neutron stars and black holes left from an intense burst of star formation. The sharp image, based on archival data from the European Southern Observatory's Wide Field Imager camera, also features spiky foreground Milky Way stars and distant background galaxies.

APOD: 2008 September 25 - The Case of the Very Dusty Binary Star
Explanation: For astronomers, close binary star system BD+20 307 originally stood out because it is extremely dusty. A substantial amount of warm dust surrounding it causes the system to appear exceptionally bright at infrared wavelengths. Of course, dust associated with planet formation is often detected around young stars, stars only a few million years old. But the BD+20 307 system has now been found to be at least a few billion years old, an age comparable to the age of our own Solar System. The large amount of warm dust is likely the debris from a relatively recent collision of planet-sized objects on the scale of, say, Earth and Venus, in the BD+20 307 system. Reminiscent of the classic scifi novel When Worlds Collide, the dramatic illustration offers a depiction of the catastrophic event. Ironically, this indirect evidence of a destructive planetary collision could also be the first indication that planetary systems can form around close binary stars. BD+20 307 is about 300 light-years distant toward the headstrong constellation Aries.

APOD: 2008 September 19 - Companion of a Young, Sun-like Star
Explanation: Located just 500 light-years away toward the constellation Scorpius, this star is only slightly less massive and a little cooler than the Sun. But it is much younger, a few million years old compared to the middle-aged Sun's 5 billion years. This sharp infrared image shows the young star has a likely companion positioned above and left - a hot planet with about 8 times the mass of Jupiter, orbiting a whopping 330 times the Earth-Sun distance from its parent star. The young planetary companion is still hot and relatively bright in infrared light due to the heat generated during its formation by gravitational contraction. In fact, such newborn planets are easier to detect before they age and cool, becoming much fainter. Though over 300 extrasolar planets have been found using other techniques, this picture likely represents the first direct image of a planet belonging to a star similar to the Sun.

APOD: 2008 September 16 - W5: Pillars of Star Creation
Explanation: How do stars form? A study of star forming region W5 by the sun-orbiting Spitzer Space Telescope provides clear clues by recording that massive stars near the center of empty cavities are older than stars near the edges. A likely reason for this is that the older stars in the center are actually triggering the formation of the younger edge stars. The triggered star formation occurs when hot outflowing gas compresses cooler gas into knots dense enough to gravitationally contract into stars. Spectacular pillars, left slowly evaporating from the hot outflowing gas, provide further visual clues. In the above scientifically-colored infrared image, red indicates heated dust, while white and green indicate particularly dense gas clouds. W5 is also known as IC 1848, and together with IC 1805 form a complex region of star formation popularly dubbed the Heart and Soul Nebulas. The above image highlights a part of W5 spanning about 2,000 light years that is rich in star forming pillars. W5 lies about 6,500 light years away toward the constellation of Cassiopeia.

APOD: 2008 August 29 - Generations of Stars in W5
Explanation: Giant star forming region W5 is over 200 light-years across and about 6,500 light-years away in the constellation Cassiopeia. W5's sculpted clouds of cold gas and dust seem to form fantastic shapes in this impressive mosaic of infrared images from the Spitzer Space Telescope. In fact, the area on the right includes the structures previously dubbed the Mountains of Creation. New evidence indicates that successive generations of stars formed in the W5 region in an expanding pattern of triggered star formation. The older, earlier generations of stars seem to cluster near the middle of the enormous cavities, with younger stars seen near the rims. Winds and radiation from the older, central stars likely carve out and compress surrounding interstellar material, triggering the collapse that gave rise to younger, later generations of stars farther out. In the false-color image, heated dust still within the cavities appears red, while the youngest stars are forming in the whitish areas. W5 is also known as IC 1848, and together with IC 1805 it is part of a complex region popularly dubbed the Heart and Soul Nebulae.

APOD: 2008 August 27 - IC 5146: The Cocoon Nebula
Explanation: Inside the Cocoon Nebula is a newly developing cluster of stars. Cataloged as IC 5146, the beautiful nebula is nearly 15 light-years wide, located some 4,000 light years away toward the northern constellation Cygnus. Like other star forming regions, it stands out in red, glowing, hydrogen gas excited by young, hot stars and blue, dust-reflected starlight at the edge of an otherwise invisible molecular cloud. In fact, the bright star near the center of this nebula is likely only a few hundred thousand years old, powering the nebular glow as it clears out a cavity in the molecular cloud's star forming dust and gas. This color view of the Cocoon Nebula traces remarkably subtle features within and surrounding the dusty stellar nursery.

APOD: 2008 July 19 - M16 and the Eagle Nebula
Explanation: Young star cluster M16 is surrounded by natal clouds of cosmic dust and glowing gas also known as The Eagle Nebula. This beautifully detailed image of the region includes fantastic shapes made famous in well-known Hubble Space Telescope close-ups of the starforming complex. Described as elephant trunks or Pillars of Creation, dense, dusty columns rising near the center are light-years in length but are gravitationally contracting to form stars. Energetic radiation from the cluster stars erodes material near the tips, eventually exposing the embedded new stars. Extending from the upper left edge of the nebula is another dusty starforming column known as the Fairy of Eagle Nebula. M16 and the Eagle Nebula lie about 7,000 light-years away, an easy target for binoculars or small telescopes in a nebula rich part of the sky toward the split constellation Serpens Cauda (the tail of the snake).

APOD: 2008 July 11 - The Far 3kpc Arm
Explanation: A major discovery was lurking in the data. By accident, while preparing a talk on the Galaxy's spiral arms for a meeting of the American Astronomical Society, Tom Dame (Harvard-Smithsonian CfA) found it - a new spiral arm in the Milky Way. The arm is labeled in this illustration as the Far 3kpc Arm, located at a distance of 3 kpc (kiloparsecs) or about 10,000 light-years from the galactic center, on the opposite side from the Sun. Along with the Near 3kpc Arm whose presence was known since the mid 1950s, the counterpart inner arms now establish that the galaxy has a simple symmetry. The arms are defined by shocked interstellar gas flowing along both sides of the Milky Way's central bar. Dame and his collaborator Patrick Thaddeus recorded the presence of both inner spiral arms in their radio data tracking emission from carbon monoxide molecules along the galactic plane. How much star formation goes on in the counterpart arms? Despite this depiction of stars and star forming regions along the arms, the last attempt to search for star formation in the Near 3kpc Arm was in 1980 and didn't turn up any. The discovery of the Far 3kpc Arm has renewed interest in this and other questions about the center of the Milky Way.

APOD: 2008 June 30 - In the Center of the Trifid Nebula
Explanation: Clouds of glowing gas mingle with dust lanes in the Trifid Nebula, a star forming region toward the constellation of Sagittarius. In the center, the three prominent dust lanes that give the Trifid its name all come together. Mountains of opaque dust appear on the right, while other dark filaments of dust are visible threaded throughout the nebula. A single massive star visible near the center causes much of the Trifid's glow. The Trifid, also known as M20, is only about 300,000 years old, making it among the youngest emission nebulae known. The nebula lies about 9,000 light years away and the part pictured here spans about 10 light years. This image was created with the 0.8-meter IAC80 telescope on the Canary Islands of Spain.

APOD: 2008 June 19 - The Star Streams of NGC 5907
Explanation: Grand tidal streams of stars seem to surround galaxy NGC 5907. The arcing structures form tenuous loops extending more than 150,000 light-years from the narrow, edge-on spiral, also known as the Splinter or Knife Edge Galaxy. Recorded only in very deep exposures, the streams likely represent the ghostly trail of a dwarf galaxy -- debris left along the orbit of a smaller satellite galaxy that was gradually torn apart and merged with NGC 5907 over four billion years ago. Ultimately this remarkable discovery image, from a small robotic observatory in New Mexico, supports the cosmological scenario in which large spiral galaxies, including our own Milky Way, were formed by the accretion of smaller ones. NGC 5907 lies about 40 million light-years distant in the northern constellation Draco.

APOD: 2008 June 5 - Spitzer's Milky Way
Explanation: The Spitzer Space Telescope's encompasing infrared view of the plane of our Milky Way Galaxy is hard to appreciate in just one picture. In fact, more than 800,000 frames of data from Spitzer's cameras have now been pieced together in an enormous mosaic of the galactic plane - the most detailed infrared picture of our galaxy ever made. The small portion seen here spans nearly 8 degrees, roughly the apparent width of your fist held at arms length, across the galaxy's center. The full mosaic is 120 degrees wide. Highlighted in the false-color presentation are curving green filaments of light from complex molecules - polycyclic aromatic hydrocarbons (PAHs) - that on Earth are the common, sooty products of incomplete combustion. The PAHs are found in star forming regions, along with reddish emission from graphite dust particles. Blue specks throughout the picture are individual Milky Way stars.

APOD: 2008 April 28 - Star Forming Region NGC 3582
Explanation: What's happening in the NGC 3582 nebula? Bright stars and interesting molecules are forming. The complex nebula resides in the star forming region called RCW 57. Visible in this image are dense knots of dark interstellar dust, bright stars that have formed in the past few million years, fields of glowing hydrogen gas ionized by these stars, and great loops of gas expelled by dying stars. A recent detailed study of NGC 3582 uncovered at least 33 massive stars in the end stages of formation, and the clear presence of the complex carbon molecules known as polycyclic aromatic hydrocarbons (PAHs). PAHs are thought to be created in the cooling gas of star forming regions, and their development in the Sun's formation nebula five billion years ago may have been an important step in the development of life on Earth. This picture was taken last year with the Blanco 4-meter telescope at the Cerro Tololo Inter-American Observatory (CTIO), in Chile.

APOD: 2008 April 18 - IC 2948: The Running Chicken Nebula
Explanation: Bright nebulae abound in and around the expansive southern constellation of Centaurus. This one, cataloged as IC 2948 is near the star Lambda Centauri and not far on the sky from the better known Eta Carinae Nebula. Embedded in the reddish glowing cloud of hydrogen gas, typical of emission nebulae found in massive star-forming regions, is the energetic young star cluster IC 2944. Seen in silhouette near the top of the view are small, dark clouds of obscuring cosmic dust. Called Thackeray's Globules for their discoverer, they are potential sites for the formation of new stars, but are likely being eroded by the intense radiation from the nearby young stars. Of course, gazing at the center of the region suggests to some IC 2948's popular name - The Running Chicken Nebula. The gorgeous skyscape spans about 70 light-years at the nebula's estimated 6,000 light-year distance.

APOD: 2008 March 26 - The NGC 3576 Nebula
Explanation: An intriguing and beautiful nebula, NGC 3576 drifts through the Sagittarius arm of our spiral Milky Way Galaxy. Within the region, episodes of star formation are thought to contribute to the complex and suggestive shapes. Powerful winds from the nebula's embedded, young, massive stars shape the looping filaments. The dramatic false-color image also highlights the contributions of hydrogen, sulfur, and oxygen, energized by intense ultraviolet radiation, to the nebular glow. But the glow also silhouettes dense clouds of dust and gas. For example, the two condensing dark clouds near the top of the picture offer potential sites for the formation of new stars. NGC 3576 itself is about 100 light-years across and 9,000 light-years away in the southern constellation of Carina, not far on the sky from the famous Eta Carinae Nebula. Near the left edge of the picture is NGC 3603, a much larger but more distant star forming region.

APOD: 2008 March 13 - Sculpting the South Pillar
Explanation: Eta Carinae, one of the most massive and unstable stars in the Milky Way Galaxy, has a profound effect on its environment. Found in the South Pillar region of the Carina Nebula, these fantastic pillars of glowing dust and gas with embedded newborn stars were sculpted by the intense wind and radiation from Eta Carinae and other massive stars. Glowing brightly in planet Earth's southern sky, the expansive Eta Carinae Nebula is a mere 10,000 light-years distant. Still, this remarkable cosmic vista is largely obscured by nebular dust and only revealed here in penetrating infrared light by the Spitzer Space Telescope. Eta Carinae itself is off the top left of the false-color image, with the bright-tipped dust pillars pointing suggestively toward the massive star's position. The Spitzer image spans almost 200 light-years at the distance of Eta Carinae.

APOD: 2008 January 9 - Hidden Galaxy IC 342 from Kitt Peak
Explanation: Beautiful nearby spiral galaxy IC 342 could be more famous if it wasn't so hidden. A sprawling island universe, IC 342 would be a prominent galaxy in our night sky, but it is almost hidden from view behind the veil of stars, gas and dust clouds in the plane of our Milky Way galaxy. Similar in size to other large, bright spiral galaxies IC 342 is a mere 7 million light-years distant in the long-necked, northern constellation of the Giraffe (Camelopardalis). Even though IC 342's light is dimmed by intervening cosmic clouds, this remarkably sharp telescopic image traces the galaxy's own obscuring dust, blue star clusters, and glowing pink star forming regions along spiral arms that wind far from the galaxy's core. IC 342 may have undergone a recent burst of star formation activity and is close enough to have gravitationally influenced the evolution of the local group of galaxies and the Milky Way.

APOD: 2007 December 15 - Mountains of Creation
Explanation: This fantastic skyscape lies at the eastern edge of giant stellar nursery W5, about 7,000 light-years away in the constellation Cassiopeia. An infrared view from the Spitzer Space Telescope, it features interstellar clouds of cold gas and dust sculpted by winds and radiation from a hot, massive star outside the picture (just above and to the right). Still swaddled within the cosmic clouds, newborn stars are revealed by Spitzer's penetrating gaze, their formation also triggered by the massive star. Fittingly dubbed "Mountains of Creation", these interstellar clouds are about 10 times the size of the analogous Pillars of Creation in M16, made famous in a 1995 Hubble Space Telescope view. W5 is also known as IC 1848 and together with IC 1805 it is part of a complex region popularly dubbed the Heart and Soul Nebulae. The Spitzer image spans about 70 light-years at the distance of W5.

APOD: 2007 December 13 - T Tauri and Hind's Variable Nebula
Explanation: The orange star centered in this remarkable telescopic skyview is T Tauri, prototype of the class of T Tauri variable stars. Nearby it is a dusty yellow cosmic cloud historically known as Hind's Variable Nebula (NGC 1555/1554). Over 400 light-years away, at the edge of a molecular cloud, both star and nebula are seen to vary significantly in brightness but not necessarily at the same time, adding to the mystery of the intriguing region. T Tauri stars are now generally recognized as young (less than a few million years old), sun-like stars still in the early stages of formation. To further complicate the picture, infrared observations indicate that T Tauri itself is part of a multiple system and suggest that the associated Hind's Nebula may also contain a very young stellar object. The dramatic color image spans about 4 light-years at the estimated distance of T Tauri.

APOD: 2007 November 22 - Pleiades and Stardust
Explanation: Hurtling through a cosmic dust cloud a mere 400 light-years away, the lovely Pleiades or Seven Sisters star cluster is well-known for its striking blue reflection nebulae. This remarkable wide-field (3 degree) image of the region shows the famous star cluster at the right, while highlighting lesser known dusty reflection nebulae nearby, across an area that would span over 20 light-years. In this case, the sister stars and cosmic dust clouds are not related, they just happen to be passing through the same region of space. But astronomers using infrared detectors have recently found a dusty disk that really does belong to one young Pleiades star -- HD 23514. Surrounding HD 23514, the disk is estimated to be comparable in size to the terrestrial planet zone in our own solar system and likely represents the debris from the process of rocky planet formation.

APOD: 2007 November 1 - Peculiar Arp 87
Explanation: A cosmic bridge of stars, gas, and dust stretches for over 75,000 light-years and joins this peculiar pair of galaxies cataloged as Arp 87. The bridge is strong evidence that these two immense star systems have passed close to each other and experienced violent tides induced by mutual gravity. As further evidence, the face-on spiral galaxy on the right, also known as NGC 3808A, exhibits many young blue star clusters produced in a burst of star formation. The twisted edge-on spiral on the left (NGC 3808B) seems to be wrapped in the material bridging the galaxies and surrounded by a curious polar ring. While such interactions are drawn out over billions of years, repeated close passages should ultimately result in the merger of this pair of galaxies into a larger single galaxy of stars. Although this scenario does look peculiar, galactic mergers are thought to be common, with Arp 87 representing a stage in this inevitable process. The Arp 87 pair are about 300 million light-years distant toward the constellation Leo. The prominent edge-on spiral at the far left appears to be a more distant background galaxy and not involved in the on-going merger.

APOD: 2007 October 19 - IC 5067 in the Pelican Nebula
Explanation: The prominent ridge of emission featured in this dramatic skyscape is cataloged as IC 5067. Part of a larger emission nebula with a distinctive shape, popularly called The Pelican Nebula, the ridge spans about 10 light-years following the curve of the cosmic pelican's head and neck. This false color view also translates the pervasive glow of narrow emission lines from atoms in the nebula to a color palette made popular in Hubble Space Telescope images of star forming regions. Fantastic, dark shapes inhabiting the 1/2 degree wide field are clouds of cool gas and dust sculpted by the winds and radiation from hot, massive stars. Close-ups of some of the sculpted clouds show clear signs of newly forming stars. The Pelican Nebula, itself cataloged as IC 5070, is about 2,000 light-years away. To find it, look northeast of bright star Deneb in the high flying constellation Cygnus.

APOD: 2007 October 18 - The Elephant's Trunk in IC 1396
Explanation: Like an illustration in a galactic Just So Story, the Elephant's Trunk Nebula winds through the emission nebula and young star cluster complex IC 1396, in the high and far off constellation of Cepheus. Of course, this cosmic elephant's trunk is over 20 light-years long. The false-color view was recorded through narrow band filters that transmit the light from hydrogen (in green), sulfur (in red), and oxygen (in blue) atoms in the region. The resulting composite highlights the bright swept-back ridges that outline pockets of cool interstellar dust and gas. Such embedded, dark, tendril-shaped clouds contain the raw material for star formation and hide protostars within the obscuring cosmic dust. Nearly 3,000 light-years distant, the relatively faint IC 1396 complex covers a large region on the sky, spanning about 5 degrees. This dramatic close-up covers a 1/2 degree wide field, about the size of the Full Moon.

APOD: 2007 October 17 - I Zwicky 18: The Case of the Aging Galaxy
Explanation: How old is this galaxy? The galaxy on the left, I Zwicky 18, was once thought to be one of the youngest galaxies on record since its bright stars indicated an age of only 500 million years. The galaxy was also intriguing because it resembled galaxies forming in the very early universe, but mysterious since it is so nearby -- only 59 million light years away -- and surrounded by galaxies that are significantly older. Recent images of I Zwicky 18 by the Hubble Space Telescope have helped resolve this mystery, discovering a population of old faint stars intermixed with the bright star population. Therefore I Zwicky 18 is now thought to be just as old as its neighbors, roughly 10 billion years old, but with an intense episode of relative new star formation. Possibly the trigger for this recent episode of bright star formation is the changing gravitational influence of I Zwicky 18's smaller companion galaxy, visible at the upper right.

APOD: 2007 October 5 - Starburst Cluster in NGC 3603
Explanation: A mere 20,000 light-years from the Sun lies NGC 3603, a resident of the nearby Carina spiral arm of our Milky Way Galaxy. NGC 3603 is well known to astronomers as one of the Milky Way's largest star-forming regions. The central open star cluster contains thousands of stars more massive than our Sun, stars that likely formed only one or two million years ago in a single burst of star formation. In fact, nearby NGC 3603 is thought to contain a convenient example of the massive star clusters that populate much more distant starburst galaxies. Surrounding the cluster are natal clouds of glowing interstellar gas and obscuring dust, sculpted by energetic stellar radiation and winds. Recorded by the Hubble's Advanced Camera for Surveys, the image spans about 17 light-years.

APOD: 2007 September 24 - A Galactic Star Forming Region in Infrared
Explanation: How do stars form? To help study this complex issue, astronomers took a deep image in infrared light of an active part of our Milky Way Galaxy where star formation is rampant. In IRDC G11.11-0.11, thick clouds of dust and gas are congealing into stars that are so dark that humans living there would see an empty night sky. The image, though, taken last year by the Spitzer Space Telescope in infrared light, shows vast glowing fields of gas and dust, indicating that much of this dust is heated by forming stars. The centers of some clouds, such as the snake-like structure on the upper left, are so thick and cold that they are dark even in infrared light. Many of the red dots are glowing dust shrouds centered on very young newly formed stars. The unusual red sphere below the snake is actually a supernova remnant, the glowing shell of a young star so massive it evolved rapidly and exploded. The region spans about 150 light years and lies about 10,000 light years away toward the constellation of Sagittarius.

APOD: 2007 September 21 - Coronet in the Southern Crown
Explanation: X-rays from young stars and infrared light from stars and cosmic dust are combined in this false color image of a star-forming region in Corona Australis, the Southern Crown. The small star grouping is fittingly known as the Coronet Cluster. A mere 420 light-years distant, the Coronet Cluster offers a relatively close-up view of stars and protostars evolving with a wide range of masses. The observations suggest that energetic x-rays come from the hot, extended stellar atmospheres or coronae of the Coronet stars. The tantalizing multi-wavelength view spans about 2 light-years and was produced using data from the orbiting Chandra Observatory (x-ray) and the Spitzer Space Telescope (infrared).

APOD: 2007 August 11 - Cosmic Tornado HH 49 50
Explanation: Light-years in length, this cosmic tornado is actually a powerful jet cataloged as HH (Herbig-Haro) 49/50 blasting down from the top of a Spitzer Space Telescope view. Though such energetic outflows are well known to be associated with the formation of young stars, the exact cause of the spiraling structures apparent in this case is still mysterious. The embryonic star responsible for the 100-kilometer per second jet is located just off the top of the picture, while the bright star seen near the tip of the jet may just by chance lie along the line of sight. In the false-color infrared image, the tornado glows with infrared light generated as the outflow heats surrounding dust clouds. The color coding shows a trend from red to blue hues at the tornado's tip indicating a systematic increase in emission at shorter wavelengths. The trend is thought to indicate an increase in molecular excitation closer to where the head of the jet is impacting interstellar gas. HH49/50 is about 450 light-years distant, located in the Chamaeleon I molecular cloud.

APOD: 2007 August 10 - Star Factory Messier 17
Explanation: Sculpted by stellar winds and radiation, the star factory known as Messier 17 lies some 5,500 light-years away in the nebula-rich constellation Sagittarius. At that distance, this 30 arcminute field of view spans almost 50 light-years. Stellar winds and energetic light from hot, massive stars formed from M17's stock of cosmic gas and dust have slowly carved away at the remaining interstellar material producing the cavernous appearance and undulating shapes. Colors in the gorgeous image were picked to emphasize light emitted by specific elements in the nebula excited by the energetic starlight. Red indicates emission from sulfur, green from hydrogen, and blue from oxygen. M17 is also known as the Omega Nebula or the Swan Nebula.

APOD: 2007 July 26 - Hot Stars in the Rosette Nebula
Explanation: Winds and radiation from massive hot stars in the Rosette Nebula have cleared the natal gas and dust from the center of the nearby star-forming region. They also pose a danger to planet forming disks around young, cooler stars in the neighborhood. This Spitzer Space Telescope infrared image of dust clouds near the Rosette's central region, shows the cleared-out cavity. The view spans about 45 light-years at the the nebula's estimated distance of 5,200 light-years. Putting your cursor over the false color picture will highlight the dangerous hot stars, classified as O stars with surface temperatures of 25,000 kelvins or higher. Astronomers calculate that cool stars wandering within about 1.6 light-years of the Rosette's O stars are in danger of having their planet forming disks destroyed.

APOD: 2007 July 14 - RCW 79: Stars in a Bubble
Explanation: A cosmic bubble of gas and dust, RCW 79 has grown to about 70 light-years in diameter, blown by the winds and radiation from hot young stars. Infrared light from the dust embedded in the nebula is tinted red in this gorgeous false-color view from the Spitzer Space Telescope. A good 17 thousand light-years away in the grand southern constellation Centaurus, the expanding nebula itself has triggered star formation as it plows into the gas and dust surrounding it. In fact, this penetrating infrared picture reveals groups of new stars as yellowish points scattered along the bubble's edge. One remarkable group still lies within its own natal bubble at about 7 o'clock (lower left), while another can be seen near the upper gap at about 3 o'clock (right) from the bubble's center.

APOD: 2007 July 10 - NGC 4449: Close-Up of a Small Galaxy
Explanation: Grand spiral galaxies often seem to get all the glory. Their newly formed, bright, blue star clusters along beautiful, symmetric spiral arms are guaranteed to attract attention. But small irregular galaxies form stars too, like NGC 4449, located about 12 million light-years away. In fact, this sharp Hubble Space Telescope close-up of the well-studied galaxy clearly demonstrates that reddish star forming regions and young blue star clusters are widespread. Less than 20,000 light-years across, the small island universe is similar in size, and often compared to our Milky Way's satellite galaxy, the Large Magellanic Cloud. NGC 4449 is a member of a group of galaxies found in the constellation Canes Venatici.

APOD: 2007 July 6 - Bright Galaxy NGC 2903
Explanation: Spiral galaxy NGC 2903 is only some 20 million light-years distant in the constellation Leo. One of the brighter galaxies visible from the northern hemisphere, it is surprisingly missing from Charles Messier's famous catalog of celestial sights. This impressively sharp color image shows off the galaxy's beautiful blue spiral arms. Included in the ground-based telescopic view are intriguing details of NGC 2903's central regions -- a remarkable mix of old and young star clusters with immense dust and gas clouds. In fact, NGC 2903 exhibits an exceptional rate of star formation activity near its center, also bright in radio, infrared, ultraviolet, and x-ray bands. Just a little smaller than our own Milky Way, NGC 2903 is about 80,000 light-years across.

APOD: 2007 May 3 - Small Galaxy NGC 4449
Explanation: Grand spiral galaxies often seem to get all the glory. Their newly formed, bright, blue star clusters along beautiful, symmetric spiral arms are guaranteed to attract attention. But small irregular galaxies form stars too, like NGC 4449, located about 12 million light-years away. The well-studied galaxy is similar in size, and often compared to our Milky Way's satellite galaxy, the Large Magellanic Cloud (LMC). This lovely color image shows NGC 4449's general bar shape, also characteristic of the LMC, with scattered young blue star clusters. Near the bottom is the pinkish glow of atomic hydrogen gas, the telltale tracer of massive star forming regions. NGC 4449 is a member of a group of galaxies found in the constellation Canes Venatici. In fact, interactions with nearby galaxies are thought to have influenced star formation in NGC 4449.

APOD: 2007 February 24- X-rays and the Eagle Nebula
Explanation: The premier Chandra X-ray Observatory images of M16, the Eagle Nebula, show many bright x-ray sources in the region. Most of the x-ray sources are energetic young stars. They are seen here as colored spots superimposed on the Hubble's well-known optical view of M16's light-year long Pillars of Creation. For example, a blue source near the tip of the large pillar at the upper left is estimated to be an embedded young star 4 or 5 times as massive as the Sun. Still, most of the x-ray sources are not coincident with the pillars themselves, indicating that embedded stars are not common in the dusty structures. The mostly empty pillars are thought to be an indication that star formation actually peaked millions of years ago within the Eagle Nebula.

APOD: 2007 January 26 - The Star Clusters of NGC 1313
Explanation: Like grains of sand on a cosmic beach, individual stars of barred spiral galaxy NGC 1313 are resolved in this sharp composite from the Hubble Space Telescope's Advanced Camera for Surveys (ACS). The inner region of the galaxy is pictured, spanning about 10,000 light-years. Hubble's unique ability to distinguish individual stars in the 14 million light-year distant galaxy has been used to unravel the fate of star clusters whose bright young stars are spread through the disk of the galaxy as the clusters dissolve. The exploration of stars and clusters in external galaxy NGC 1313 offers clues to star formation and star cluster evolution in our own Milky Way.

APOD: 2007 January 10 - NGC 602 and Beyond
Explanation: Near the outskirts of the Small Magellanic Cloud, a satellite galaxy some 200 thousand light-years distant, lies 5 million year young star cluster NGC 602. Surrounded by natal gas and dust, NGC 602 is featured in this stunning Hubble image of the region. Fantastic ridges and swept back shapes strongly suggest that energetic radiation and shock waves from NGC 602's massive young stars have eroded the dusty material and triggered a progression of star formation moving away from the cluster's center. At the estimated distance of the Small Magellanic Cloud, the picture spans about 200 light-years, but a tantalizing assortment of background galaxies are also visible in the sharp Hubble view. The background galaxies are hundreds of millions of light-years or more beyond NGC 602.

APOD: 2006 November 30 - A Pelican in the Swan
Explanation: The Pelican Nebula lies about 2,000 light-years away in the high flying constellation Cygnus, the Swan. Also known as IC 5070, this cosmic pelican is appropriately found just off the "east coast" of the North America Nebula (NGC 7000), another surprisingly familiar looking emission nebula in Cygnus. The Pelican and North America nebulae are part of the same large and complex star forming region, almost as nearby as the better-known Orion Nebula. From our vantage point, dark dust clouds (upper left) help define the Pelican's eye and long bill, while a bright front of ionized gas suggests the curved shape of the head and neck. Based on digitized black and white images from the Samuel Oschin Telescope at Palomar Observatory, this striking synthesized color view includes two bright foreground stars and spans about 30 light-years at the estimated distance of the Pelican Nebula.

APOD: 2006 October 22 - Star EGGs in the Eagle Nebula
Explanation: Where do stars form? One place, star forming regions known as "EGGs", are uncovered at the end of this giant pillar of gas and dust in the Eagle Nebula (M16). EGGs, short for evaporating gaseous globules, are dense regions of mostly molecular hydrogen gas that fragment and gravitationally collapse to form stars. Light from the hottest and brightest of these new stars heats the end of the pillar and causes further evaporation of gas - revealing yet more EGGs and more young stars. This picture was taken by the Wide Field and Planetary Camera on board the Hubble Space Telescope.

APOD: 2006 October 5 - Hidden Galaxy IC 342
Explanation: Similar in size to other large, bright spiral galaxies IC 342 is a mere 7 million light-years distant in the long-necked, northern constellation Camelopardalis. A sprawling island universe, IC 342 would otherwise be a prominent galaxy in our night sky, but it is almost hidden from view behind the veil of stars, gas and dust clouds in the plane of our Milky Way galaxy. Even though IC 342's light is dimmed by intervening cosmic clouds, this remarkably sharp telescopic image traces the galaxy's own obscuring dust, blue star clusters, and glowing pink star forming regions along spiral arms that wind far from the galaxy's core. IC 342 may have undergone a recent burst of star formation activity and is close enough to have gravitationally influenced the evolution of the local group of galaxies and the Milky Way.

APOD: 2006 August 18 - Spitzer's Orion
Explanation: Few cosmic vistas excite the imagination like the Orion Nebula, an immense stellar nursery some 1,500 light-years away. Also known as M42, the nebula is visible to the unaided eye, but this stunning infrared view from the Spitzer Space Telescope penetrates the turbulent cosmic gas and dust clouds to explore the region in unprecedented detail. At full resolution, the remarkable image data yields a census of new stars and potential solar systems. About 2,300 young stars surrounded by planet-forming disks were detected based on the infrared glow of their warm dust, along with about 200 stellar embryos, stars too young to have developed disks. This 0.8 by 1.4 degree false-color image is about 20 light-years wide at the distance of the Orion Nebula.

APOD: 2006 August 15 - IC 410 and NGC 1893
Explanation: A faint, dusty rose of the northern sky, emission nebula IC 410 lies about 12,000 light-years away in the constellation Auriga. The cloud of glowing hydrogen gas is over 100 light-years across, sculpted by stellar winds and radiation from embedded open star cluster NGC 1893. Formed in the interstellar cloud a mere 4 million years ago, bright cluster stars are seen just below the prominent dark dust cloud near picture center. Notable near the 7 o'clock position in this wide, detailed view are two relatively dense streamers of material trailing away from the nebula's central regions. Potentially sites of ongoing star formation, these cosmic tadpole shapes are about 10 light-years long.

APOD: 2006 April 21 - NGC 253: Dusty Island Universe
Explanation: Shiny NGC 253, sometimes called the Silver Dollar Galaxy, is one of the brightest spiral galaxies visible - and also one of the dustiest. First swept up in 1783 by mathematician and astronomer Caroline Herschel, the dusty island universe lies a mere 10 million light-years away in the southern constellation Sculptor. About 70 thousand light-years across, NGC 253 is the largest member of the Sculptor Group of Galaxies, the nearest to our own Local Group of Galaxies. In addition to its spiral dust lanes, striking tendrils of dust seem to be rising from the galactic disk in this gorgeous view. The high dust content accompanies frantic star formation, giving NGC 253 the designation of a starburst galaxy. NGC 253 is also known to be a strong source of high-energy x-rays and gamma rays, likely due to massive black holes near the galaxy's center.

APOD: 2006 April 14 - Smoke from the Cigar Galaxy
Explanation: Very bright in infrared light, well-known starburst galaxy M82's popular name describes its suggestive shape seen at visible wavelengths - The Cigar Galaxy. Ironically, M82's fantastic appearance in this Spitzer Space Telescope image really is due to cosmic "smoke" - the infrared emission of exented dust features blown by stellar winds from M82's luminous, central star forming regions. The false-color view highlights a component of dust emission from complex carbon molecules called polycyclic aromatic hydrocarbons or PAHs. PAHs are also seen in star forming regions throughout our own, much calmer, Milky Way Galaxy and are products of combustion on planet Earth. Likely triggered by interactions with nearby galaxy M81, M82's intense star formation activity appears to be blowing out immense clouds of dust and PAHs extending nearly 20,000 light-years both above and below the galactic plane. M82 is about 12 million light-years away in the constellation Ursa Major.

APOD: 2006 February 3 - Cosmic Tornado HH 49 50
Explanation: Light-years in length, this cosmic tornado is actually a powerful jet cataloged as HH (Herbig-Haro) 49/50 blasting down from the top of a Spitzer Space Telescope view. Though such energetic outflows are well known to be associated with the formation of young stars, the exact cause of the spiraling structures apparent in this case is still mysterious. The embryonic star responsible for the 100-kilometer per second jet is located just off the top of the picture, while the bright star seen near the tip of the jet may just by chance lie along the line of sight. In the false-color infrared image, the tornado glows with infrared light generated as the outflow heats surrounding dust clouds. The color coding shows a trend from red to blue hues at the tornado's tip indicating a systematic increase in emission at shorter wavelengths. The trend is thought to indicate an increase in molecular excitation closer to where the head of the jet is impacting interstellar gas. HH49/50 is about 450 light-years distant, located in the Chamaeleon I molecular cloud.

APOD: 2006 January 30 - NGC 1999: South of Orion
Explanation: South of the large star-forming region known as the Orion Nebula, lies bright blue reflection nebula NGC 1999. The nebula is marked with a dark inverted T-shape at the lower left in a broad cosmic vista that spans over 10 light-years. The dark shape is a dense gas and dust cloud, or Bok globule, seen in silhouette against the bright nebula, and likely a site of future star formation. At the edge of the Orion molecular cloud complex some 1,500 light-years distant, NGC 1999's illumination is provided by the embedded variable star V380 Orionis. The region abounds with energetic young stars producing jets and outflows that create luminous shock waves, including HH (Herbig-Haro) 1 and 2 just below and left of NGC 1999, and the apparent cascade of reddish arcs and bow shocks beginning at the upper right. The stellar jets and outflows push through the surrounding material at speeds of hundreds of kilometers per second.

APOD: 2006 January 20 - LL Ori and the Orion Nebula
Explanation: This esthetic close-up of cosmic clouds and stellar winds features LL Orionis, interacting with the Orion Nebula flow. Adrift in Orion's stellar nursery and still in its formative years, variable star LL Orionis produces a wind more energetic than the wind from our own middle-aged Sun. As the fast stellar wind runs into slow moving gas a shock front is formed, analogous to the bow wave of a boat moving through water or a plane traveling at supersonic speed. The small, arcing, graceful structure just above and left of center is LL Ori's cosmic bow shock, measuring about half a light-year across. The slower gas is flowing away from the Orion Nebula's hot central star cluster, the Trapezium, located off the upper left corner of the picture. In three dimensions, LL Ori's wrap-around shock front is shaped like a bowl that appears brightest when viewed along the "bottom" edge. The beautiful picture is part of a large mosaic view of the complex stellar nursery in Orion, filled with a myriad of fluid shapes associated with star formation.

APOD: 2006 January 18 - Cartwheel Of Fortune
Explanation: By chance, a collision of two galaxies has created a surprisingly recognizable shape on a cosmic scale - The Cartwheel Galaxy. The Cartwheel is part of a group of galaxies about 400 million light years away in the constellation Sculptor (two smaller galaxies in the group are visible below and left). Its rim is an immense ring-like structure over 100,000 light years in diameter, composed of star forming regions filled with extremely bright, massive stars. When galaxies collide they pass through each other, their individual stars do not come into contact. However, this ring-like shape is the result of gravitational disruption caused by a smaller galaxy passing through a large one, compressing the interstellar gas and dust and causing a star formation wave to move out like a ripple across the surface of a pond. This false-color composite image of the Cartwheel Galaxy is from space-based observatories. The Chandra X-ray Observatory data is in purple, the Galaxy Evolution Explorer ultraviolet view is in blue, the Hubble Space Telescope visible light picture is in green and the Spitzer Space Telescope infrared image is in red.

APOD: 2006 January 6 - The Tarantula Nebula
Explanation: First cataloged as a star, 30 Doradus is actually an immense star forming region in nearby galaxy The Large Magellanic Cloud. The region's spidery appearance is responsible for its popular name, the Tarantula Nebula, except that this tarantula is about 1,000 light-years across, and 180,000 light-years away in the southern constellation Dorado. If the Tarantual Nebula were at the distance of the Orion Nebula (1,500 light-years), the nearest stellar nursery to Earth, it would appear to cover about 30 degrees on the sky or 60 full moons. The spindly arms of the Tarantula Nebula surround NGC 2070, a cluster that contains some of the intrinsically brightest, most massive stars known. Intriguing details of the nebula's core can be seen in this remarkable skyscape, a composite of 31 hours of exposure time. This cosmic Tarantula also lies near the site of the closest recent supernova.

APOD: 2005 December 23 - Hydrogen and Dust in the Rosette Nebula
Explanation: At the edge of a large molecular cloud in Monoceros, some 3,000 light years away, dark filaments of dust are silhouetted by luminous hydrogen gas. The close up view of the Rosette Nebula dramatically suggests that star formation is an on going process in the region, with dark filaments sculpted by winds and radiation from hot, young stars. Ultraviolet radiation from the young stars also strips electrons from the surrounding hydrogen atoms. As electrons and atoms recombine they emit longer wavelength, lower energy light in a well known characteristic pattern of bright spectral lines. At visible wavelengths, the strongest emission line in this pattern is in the red part of the spectrum and is known as "Hydrogen-alpha" or just H-alpha. Part of IPHAS, a survey of H-alpha emission in our Milky Way Galaxy, this image spans about 25 light-years.

APOD: 2005 November 17 - Young Stars of NGC 346
Explanation: Star cluster NGC 346 is embedded in the largest star forming region in the Small Magellanic Cloud, some 210,000 light-years distant. The massive stars of NGC 346 are short lived, but very energetic. Their winds and radiation sweep out an interstellar cavern in the gas and dust cloud about 200 light-years across, triggering star formation and sculpting the region's dense inner edge. Cataloged as N66, the star forming region also appears to contain a large population of infant stars. A mere 3 to 5 million years old and not yet burning hydrogen in their cores, the infant stars are strewn about the embedded star cluster. In the false-color Hubble Space Telescope image, visible and near-infrared light are seen as blue and green, while light from atomic hydrogen emission is red.

APOD: 2005 November 11 - Mountains of Creation
Explanation: This fantastic skyscape lies at the eastern edge of giant stellar nursery W5, about 7,000 light-years away in the constellation Cassiopeia. An infrared view from the Spitzer Space Telescope, it features interstellar clouds of cold gas and dust sculpted by winds and radiation from a hot, massive star outside the picture (just above and to the right). Still swaddled within the cosmic clouds, newborn stars are revealed by Spitzer's penetrating gaze, their formation also triggered by the massive star. Fittingly dubbed "Mountains of Creation", these interstellar clouds are about 10 times the size of the analogous Pillars of Creation in M16, made famous in a 1995 Hubble Space Telescope view. W5 is also known as IC 1848 and together with IC 1805 it is part of a complex region popularly dubbed the Heart and Soul Nebulae. The Spitzer image spans about 70 light-years at the distance of W5.

APOD: 2005 October 17 - Short Gamma Ray Bursts Localized
Explanation: What causes gamma-ray bursts? The most energetic type of explosions known in the cosmos has been an enigma since discovered over 30 years ago. It now appears that there may not be one unique type of progenitor. Long duration gamma-ray bursts (GRBs) have been localized, over the past few years, to blue regions in the universe rich in star formation. Massive young stars nearing the end of their short lives commonly explode in these regions. Astronomers associate these long duration GRBs, that can last from seconds to minutes, with a type of stellar explosion common in young massive stars. Over the past few months, short duration GRBs have finally been localized and found to occur in different types of regions -- not only blue regions rich in star formation. Many astronomers therefore now theorize that short GRBs, which typically last less than one second, are the result of a different progenitor process than long GRBs. A leading model is that a short GRB will occur when a neutron star either impacts another neutron star or a black hole. Such collisions may occur well after star-forming regions have otherwise burned out. Pictured in the above illustration, two energized neutrons stars finally approach each other in their orbits, a death spiral that might end with a short GRB.

APOD: 2005 September 30 - IC 1396 H-Alpha Close-Up
Explanation: Clouds of glowing hydrogen gas mingle ominously with dark dust lanes in this close-up of IC 1396, an active star forming region some 2,000 light years away in the constellation Cepheus. In this and other similar emission nebulae, energetic ultraviolet light from a hot young star strips electrons from the surrounding hydrogen atoms. As the electrons and atoms recombine they emit longer wavelength, lower energy light in a well known characteristic pattern of bright spectral lines. At visible wavelengths, the strongest emission line in this pattern is in the red part of the spectrum and is known as "Hydrogen-alpha" or just H-alpha. Part of IPHAS, a survey of H-alpha emission in our Milky Way Galaxy, this image spans about 20 light-years and highlights bright, dense regions within IC 1396, likely sites where massive new stars are born.

APOD: 2005 September 27 - The Star Pillars of Sharpless 171
Explanation: Towering pillars of cold gas and dark dust adorn the center star forming region of Sharpless 171. An open cluster of stars is forming there from the gas in cold molecular clouds. As energetic light emitted by young massive stars boils away the opaque dust, the region fragments and picturesque pillars of the remnant gas and dust form and slowly evaporate. The energetic light also illuminates the surrounding hydrogen gas, energize it to glow as a red emission nebula. Pictured above is the active central region of the Sharpless 171 greater emission nebula. Sharpless 171 incorporates NGC 7822 and the active region Cederblad 214, much of which is imaged above. The area above spans about 20 light years, lies about 3,000 light years away, and can be seen with a telescope toward the northern constellation of the King of Ethiopia (Cepheus).

APOD: 2005 September 24 - Cat s Eye
Explanation: Staring across interstellar space, the alluring Cat's Eye nebula lies three thousand light-years from Earth. A classic planetary nebula, the Cat's Eye (NGC 6543) represents a final, brief yet glorious phase in the life of a sun-like star. This nebula's dying central star may have produced the simple, outer pattern of dusty concentric shells by shrugging off outer layers in a series of regular convulsions. But the formation of the beautiful, more complex inner structures is not well understood. Seen so clearly in this sharp Hubble Space Telescope image, the truly cosmic eye is over half a light-year across. Of course, gazing into the Cat's Eye, astronomers may well be seeing the fate of our sun, destined to enter its own planetary nebula phase of evolution ... in about 5 billion years.

APOD: 2005 September 23 - Portrait of RY Tauri
Explanation: A star emerges from its natal cloud of gas and dust in this tantalizing portrait of RY Tauri, a small stellar nursery at the edge of the Taurus molecular cloud, a mere 450 light-years away. Illuminating a region that spans about 2/3 of a light-year, the youthful, central star is large, cool, and known to vary in brightness. Still collapsing, in a few million years the star's winds will likely clear out the gas and dust clouds, as it settles down to become a steady main sequence star like the Sun. What remains could well include a planetary system. The image data for RY Tauri is from the Gemini Observatory, on Mauna Kea, Hawaii -- based on observations proposed by the Astronomy Club of Dorval, Quebec.

APOD: 2005 September 8 - IC 1396 in Cepheus
Explanation: Stunning emission nebula IC 1396 mixes glowing cosmic gas and dark dust clouds in the high and far off constellation of Cepheus. Energized by the bright, bluish central star seen here, this star forming region sprawls across hundreds of light-years -- spanning over three degrees on the sky while nearly 3,000 light-years from planet Earth. Among the intriguing dark shapes within IC 1396, the winding Elephant's Trunk nebula lies just below center. The gorgeous color view is a composition of digitized black and white photographic plates recorded through red and blue astronomical filters. The plates were taken using the Samuel Oschin Telescope, a wide-field survey instrument at Palomar Observatory, between 1989 and 1993.

APOD: 2005 August 23 - NGC 281: The Pacman Nebula
Explanation: NGC 281 is a busy workshop of star formation. Prominent features include a small open cluster of stars, a diffuse red-glowing emission nebula, large lanes of obscuring gas and dust, and dense knots of dust and gas in which stars may still be forming. The open cluster of stars IC 1590 visible around the center has formed only in the last few million years. The brightest member of this cluster is actually a multiple-star system shining light that helps ionize the nebula's gas, causing the red glow visible throughout. The lanes of dust visible left of center are likely homes of future star formation. Particularly striking in the above photograph are the dark Bok globules visible against the bright nebula. The NGC 281 system, dubbed the Pacman nebula for its overall shape, lies about 10 thousand light years distant.

APOD: 2005 August 5 - HD 188753: Triple Sunset
Explanation: Although it looks like fiction, this artist's vision of sunset on an alien world is based on fact -- the recent discovery of a hot, jupiter-sized planet orbiting in triple star system HD 188753. Only 149 light-years away in the constellation Cygnus, HD 188753's massive planet was detected by astronomer Maciej Konacki after analyzing detailed spectroscopic data from the Keck Observatory. The large planet itself is depicted at the upper left in this imagined view from the well-illuminated surface of a hypothetical rocky moon. From this perspective, the closest, hottest and most massive star in the triple system, a star only a little hotter than the Sun, has set below distant peaks. The two other suns nearing the horizon are both cooler and farther from the large planet. While other hot, jupiter-like planets are known to orbit nearby stars, the "crowded" multiple star nature of this system challenges current theories of planet formation.

APOD: 2005 June 21 - The Cygnus Wall of Star Formation
Explanation: The North America Nebula in the sky can do what North Americans on Earth cannot -- form stars. Specifically, in analogy to the Earth-confined continent, the bright part that appears as Central America and Mexico is actually a hot bed of gas, dust, and newly formed stars known as the Cygnus Wall. The above image in representative colors shows the star forming wall lit and eroded by bright young stars, and partly hidden by the dark dust they have created. The part of the North America nebula (NGC 7000) shown spans about 15 light years and lies about 1,500 light years away toward the constellation of Cygnus.

APOD: 2005 June 2 - Sculpting the South Pillar
Explanation: Eta Carinae, one of the most massive and unstable stars in the Milky Way Galaxy, has a profound effect on its environment. Found in the the South Pillar region of the Carina Nebula, these fantastic pillars of glowing dust and gas with embedded newborn stars were sculpted by the intense wind and radiation from Eta Carinae and other massive stars. Glowing brightly in planet Earth's southern sky, the expansive Eta Carinae Nebula is a mere 10,000 light-years distant. Still, this remarkable cosmic vista is largely obscured by nebular dust and only revealed here in penetrating infrared light by the Spitzer Space Telescope. Eta Carinae itself is off the top left of the false-color image, with the bright-tipped dust pillars pointing suggestively toward the massive star's position. The Spitzer image spans almost 200 light-years at the distance of Eta Carinae.

APOD: 2005 May 21 - Snake in the Dark
Explanation: Dark nebulae snake across a gorgeous expanse of stars in this wide-field view toward the pronounceable constellation Ophiuchus and the center of our Milky Way Galaxy. In fact, the central S-shape seen here is well known as the Snake Nebula. It is also listed as Barnard 72 (B72), one of 182 dark markings of the sky cataloged in the early 20th century by astronomer E. E. Barnard. Unlike bright emission nebulae and star clusters, Barnard's nebulae are interstellar dark clouds of obscuring gas and dust. Their shapes are visible in cosmic silhouette only because they lie in the foreground along the line of sight to rich star fields and glowing stellar nurseries near the plane of our Galaxy. Many of Barnard's dark nebulae are themselves likely sites of future star formation. Barnard 72 is a few light years across and about 650 light years away.

APOD: 2005 April 15 - RCW 79: Stars in a Bubble
Explanation: A cosmic bubble of gas and dust, RCW 79 has grown to about 70 light-years in diameter, blown by the winds and radiation from hot young stars. Infrared light from the dust embedded in the nebula is tinted red in this gorgeous false-color view from the Spitzer Space Telescope. A good 17 thousand light-years away in the grand southern constellation Centaurus, the expanding nebula itself has triggered star formation as it plows into the gas and dust surrounding it. In fact, this penetrating infrared picture reveals groups of new stars as yellowish points scattered along the bubble's edge. One remarkable group still lies within its own natal bubble at about 7 o'clock (lower left), while another can be seen near the upper gap at about 3 o'clock (right) from the bubble's center.

APOD: 2005 April 2 - Cyg X-1: Can Black Holes Form in the Dark?
Explanation: The formation of a black hole from the collapsing core of a massive star is thought to be heralded by a spectacular supernova explosion. Such an extremely energetic collapse is also a leading explanation for the mysterious cosmic gamma-ray bursts. But researchers now suggest that the Milky Way's most famous black hole, Cygnus X-1, was born when a massive star collapsed -- without any supernova explosion at all. Their dynamical evidence is summarized in this color image of a gorgeous region in Cygnus, showing Cyg X-1 and a cluster of massive stars (yellow circles) known as Cygnus OB3. Arrows compare the measured direction and speed of Cyg X-1 and the average direction and speed of the massive stars of Cyg OB3. The similar motions indicate that Cyg X-1's progenitor star was itself a cluster member and that its path was not altered at all when it became a black hole. In contrast, if Cyg X-1 were born in a violent supernova it would have likely received a fierce kick, changing its course. If not a supernova, could the formation of the Cyg X-1 black hole have produced a dark gamma-ray burst in the Milky Way?

APOD: 2005 March 4 - NGC 1427A: Galaxy in Motion
Explanation: In this tantalizing image, young blue star clusters and pink star-forming regions abound in NGC 1427A, a galaxy in motion. The small irregular galaxy's swept back outline points toward the top of this picture from the Hubble Space Telescope - and that is indeed the direction NGC 1427A is moving as it travels toward the center of the Fornax cluster of galaxies, some 62 million light-years away. Over 20,000 light-years long and similar to the nearby Large Magellanic Cloud, NGC 1427A is speeding through the Fornax cluster's intergalactic gas at around 600 kilometers per second. The resulting pressure is giving the galaxy its arrowhead outline and triggering the beautiful but violent episodes of star formation. Still, it is understood that interactions with cluster gas and the other cluster galaxies during its headlong flight will ultimately disrupt galaxy NGC 1427A. Many unrelated background galaxies are visible in the sharp Hubble image, including a striking face-on spiral galaxy at the upper left.

APOD: 2005 March 1 - NGC 1531/2: Interacting Galaxies
Explanation: This dramatic image of an interacting pair of galaxies was made using 8-meter Gemini South telescope at Cerro Pachon, Chile. NGC 1531 is the background galaxy with a bright core just above center and NGC 1532 is the foreground spiral galaxy laced with dust lanes. The pair is about 55 million light-years away in the southern constellation Eridanus. These galaxies lie close enough together so that each feels the influence of the other's gravity. The gravitational tug-of-war has triggered star formation in the foreground spiral as evidenced by the young, bright blue star clusters along the upper edge of the front spiral arm. Though the spiral galaxy in this pair is viewed nearly edge-on, astronomers believe the system is similar to the face-on spiral and companion known as M51, the Whirlpool Galaxy.

APOD: 2005 January 25 - NGC 6946: The Fireworks Galaxy
Explanation: Why is this galaxy so active? Nearby spiral galaxy NGC 6946 is undergoing a tremendous burst of star formation with no obvious cause. In many cases spirals light up when interacting with another galaxy, but NGC 6946 appears relatively isolated in space. Located just 10 million light years away toward the constellation of Cepheus, this beautiful face-on spiral spans about 20,000 light years and is seen through a field of foreground stars from our Milky Way Galaxy. The center of NGC 6946 is home to a nuclear starburst itself, and picturesque dark dust is seen lacing the disk along with bright blue stars, red emission nebulas, fast moving gas clouds, and unusually frequent supernovas. The 8-meter Gemini North Telescope in Hawaii, USA, took the above image. A suggested explanation for the high star formation rate is the recent accretion of many primordial low-mass neutral hydrogen clouds from the surrounding region.

APOD: 2004 November 1 - Spooky Star Forming Region DR 6
Explanation: How could stars form such a spooky and familiar shape as a human skull? First, the complex process of star formation creates nebulas of many shapes and sizes -- it is human perception that identifies the skull shape. Next, the physical reasons for the large nearly empty cavities that resemble the skull's eyes and mouth in nebula DR 6 are the strong stellar winds and energetic light emanating from about ten bright young stars in the nebula's central "nose". The length of the central nasal bridge is about 3.5 light years. Star forming nebula DR 6 is located about 4000 light years away toward the constellation of Cygnus. The Spitzer Space Telescope took the above image last year in four infrared colors. The perhaps-perceived eeriness of nebula DR 6 commemorates today being historically spooky All Hallow's Day, which follows All Hallow's Eve or "Halloween".

APOD: 2004 October 20 - NGC 281: Cluster, Clouds, and Globules
Explanation: NGC 281 is a busy workshop of star formation. Prominent features include a small open cluster of stars, a diffuse red-glowing emission nebula, large lanes of obscuring gas and dust, and dense knots of dust and gas in which stars may still be forming. The open cluster of stars IC 1590 visible around the center has formed only in the last few million years. The brightest member of this cluster is actually a multiple-star system shining light that helps ionize the nebula's gas, causing the red glow visible throughout. The lanes of dust visible left of center are likely homes of future star formation. Particularly striking in the above photograph are the dark Bok globules visible against the bright nebula. The entire NGC 281 system lies about 10 thousand light years distant.

APOD: 2004 October 16 - The Bubbling Cauldron of NGC 3079
Explanation: Edge-on spiral galaxy NGC 3079 is a mere 50 million light-years away toward the constellation Ursa Major. Shown in this stunning false-color Hubble Space Telescope image, the galaxy's disk - composed of spectacular star clusters in winding spiral arms and dramatic dark lanes of dust - spans some 70,000 light-years. Still, NGC 3079's most eye-catching features are the pillars of gas which tower above a swirling cosmic cauldron of activity at the galaxy's center. Seen in the close-up inset at lower right, the pillars rise to a height of about 2,000 light-years and seem to lie on the surface of an immense bubble rising from the galactic core. Measurements indicate that the gaseous pillars are streaming away from the core at 6 million kilometers per hour. What makes this galaxy's cauldron bubble? Astronomers are exploring the possibility that the superbubble is formed by winds from massive stars. If so, these massive stars were likely born all at once as the galactic center underwent a sudden burst of star formation.

APOD: 2004 September 10 - Cat's Eye
Explanation: Staring across interstellar space, the alluring Cat's Eye nebula lies three thousand light-years from Earth. A classic planetary nebula, the Cat's Eye (NGC 6543) represents a final, brief yet glorious phase in the life of a sun-like star. This nebula's dying central star may have produced the simple, outer pattern of dusty concentric shells by shrugging off outer layers in a series of regular convulsions. But the formation of the beautiful, more complex inner structures is not well understood. Seen so clearly in this sharp Hubble Space Telescope image, the truly cosmic eye is over half a light-year across. Of course, gazing into the Cat's Eye, astronomers may well be seeing the fate of our sun, destined to enter its own planetary nebula phase of evolution ... in about 5 billion years.

APOD: 2004 August 28- M17: A Hubble Close-Up
Explanation: Sculpted by stellar winds and radiation, these fantastic, undulating shapes lie within the stellar nursery known as M17, the Omega Nebula, some 5,500 light-years away in the nebula-rich constellation Sagittarius. The lumpy features in the dense cold gas and dust are illuminated by stars off the upper left of the image and may themselves represent sites of future star formation. Colors in the fog of surrounding hotter material indicate M17's chemical make up. The predominately green glow corresponds to abundant hydrogen, with trace sulfur and oxygen atoms contributing red and blue hues. The picture spans about 3 light-years and was released in the thirteenth year of the Hubble Space Telescope's cosmic voyage of exploration.

APOD: 2004 July 7 - N11B: Star Cloud of the LMC
Explanation: Massive stars, abrasive winds, mountains of dust, and energetic light sculpt one of the largest and most picturesque regions of star formation in the Local Group of Galaxies. Known as N11, the region is visible on the upper right of many images of its home galaxy, the Milky Way neighbor known as the Large Magellanic Clouds (LMC). The above image actually highlights N11B, part of the nebula that spans about 100 light years and is particularly active. The entire emission nebula N11 is second in LMC size only to 30 Doradus. Studying the stars in N11B has shown that it actually houses three successive generations of star formation. Compact globules of dark dust housing emerging young stars are also visible on the upper right.

APOD: 2004 June 3 - Cosmic Construction Zone RCW 49
Explanation: Stars and planets appear to be under construction in dusty nebula RCW 49. This Spitzer Space Telescope false-color infrared view of the nearby stellar nursery shows that known, hot stars are well on their way to clearing out the nebula's central regions. But it also uncovers more than 300 newborn stars, seen here strewn throughout the cosmic dust clouds and filaments. The infrared data indicate the likely presence of protoplanetary discs around some of the infant suns, among the faintest and farthest potential planet-forming discs ever observed. Such exciting results give further support to the idea that planet-forming discs are a natural part of a star's evolution. A mere 14,000 light-years away toward the constellation Centaurus, the industrious RCW 49 is about 350 light-years across.

APOD: 2004 June 1 - The Supergalactic Wind from Starburst Galaxy M82
Explanation: Star formation occurs at a faster pace in M82 -- a galaxy with about ten times the rate of massive star birth (and death) compared to our Milky Way. Winds from massive stars and blasts from supernova explosions have created a billowing cloud of expanding gas from this remarkable starburst galaxy. The above scientifically color-coded image highlights the complexity and origin of the plume by combining a wide field image from the WIYN Telescope in Arizona with a smaller high-resolution image from the orbiting Hubble Space Telescope. M82's aspect in optical pictures has led to its popular moniker, the Cigar Galaxy. M82's burst of star formation was likely triggered a mere 100 million years ago in the latest of a series of bouts with neighboring large galaxy M81.

APOD: 2004 May 29 - Cone Nebula Close Up
Explanation: Cones, pillars, and majestic flowing shapes abound in stellar nurseries where natal clouds of gas and dust are buffeted by energetic winds from newborn stars. A well-known example, the Cone Nebula within the bright galactic star-forming region NGC 2264, was captured in this close-up view from the Hubble Space Telescope's Advanced Camera for Surveys. While the Cone Nebula, about 2,500 light-years away in Monoceros, is around 7 light-years long, the region pictured here surrounding the cone's blunted head is a mere 2.5 light-years across. In our neck of the galaxy that distance is just over half way from the Sun to its nearest stellar neighbor, Alpha Centauri. The massive star NGC 2264 IRS, seen by Hubble's infrared camera in 1997, is the likely source of the wind sculpting the Cone Nebula and lies off the top of the image. The Cone Nebula's reddish veil is produced by glowing hydrogen gas.

APOD: 2004 May 20 - Sharpless 140
Explanation: Three young, massive stars will eventually emerge from this natal cloud of dust and gas, but their presence is already revealed in this false-color image from the Spitzer Space Telescope. The picture offers a penetrating infrared view of an emission nebula cataloged as Sharpless 140 which lies about 3,000 light-years away toward the constellation Cepheus. The young stars are otherwise obscured in visible light images by the dusty environs. Sculpted by winds and radiation from hot stars in the region, the majestic arcing structures pictured here are tens of light-years across and contain surprisingly complex molecules - polycyclic aromatic hydrocarbons (PAHs) - that glow in the infrared. An amazingly detailed record of cosmic markers of star formation, the image hints at the wealth of infrared data now freely available in the Spitzer Space Telescope archive.

APOD: 2004 May 17 - NGC 3372: The Great Nebula in Carina
Explanation: In one of the brightest parts of the Milky Way lies a nebula where some of the oddest things occur. NGC 3372, known as the Great Nebula in Carina, is home to massive stars and changing nebula. Eta Carina, the most energetic star in the nebula was one of the brightest stars in the sky in the 1830s, but then faded dramatically. The Keyhole Nebula, visible near the center, houses several of the most massive stars known and has also changed its appearance. The Carina Nebula spans over 300 light years and lies about 7000 light-years away in the constellation of Carina. The above image was taken from La Frontera in Alcohuaz, Chile. Eta Carina might explode in a dramatic supernova within the next thousand years, and has even flared in brightness over just the past decade.

APOD: 2004 April 14 - Massive Star Forming Region DR21 in Infrared
Explanation: Deep in the normally hidden recesses of giant molecular cloud DR21, a stellar nursery has been found creating some of the most massive stars yet recorded. The orbiting Spitzer Space Telescope's Infrared Array Camera opened the window into the cloud last year in mid- infrared light. The cloud is opaque to visible light because of dense interstellar dust. Noticeable in the above representative color infrared Spitzer image are huge bubbles, a complex tapestry of dust and gas, and very massive stars. The infrared filaments actually glow because of organic compounds known as PAHs. The intricate patterns are caused by complex interactions between interstellar winds, radiation pressures, magnetic fields, and gravity. The pictured region spans about 75 light years and lies about 6,000 light years distant toward the constellation of Cygnus.

APOD: 2004 March 11 - Henize 206: Cosmic Generations
Explanation: Peering into a dusty nebula in nearby galaxy the Large Magellanic Cloud, infrared cameras on board the Spitzer Space Telescope recorded this detailed view of stellar nursery Henize 206 filled with newborn stars. The stars appear as white spots within the swirls of dust and gas in the false-color infrared image. Near the top, the sweeping telltale arcs of a supernova remnant are also visible, expanding debris from the final explosion of a massive star. The proximity of the ancient supernova indicates that the shockwave from that stellar death explosion itself likely triggered the formation of the new generation of emerging stars, compressing the gas and dust within Henize 206 and continuing the cosmic cycle of star death and star birth. At the distance of the Large Magellanic Cloud, about 163,000 light-years, this image covers an area about 1,000 light-years across.

APOD: 2004 February 19 - McNeil's Nebula
Explanation: It was a clear, cold western Kentucky night on January 23rd as seasoned amateur astronomer Jay McNeil tried out his recently acquired 3-inch refracting telescope by imaging the area around a familiar object, the M78 reflection nebula in Orion. Days later while processing the images, he noted a substantial but totally unfamiliar nebulosity in the region! With a little help from his friends, his amazing discovery is now recognized as a newly visible reflection nebula surrounding a newborn star -- McNeil's Nebula. Pictured here at the center of this close-up, McNeil's Nebula with its illuminating young star at the tip, do not appear in images of the area before September 2003. The emergence of McNeil's Nebula is a rare event to witness and astronomers are eagerly following its development, but Orion will soon lie too close to the Sun in the sky, interrupting further observations for several months. The Orion nebula complex itself is around 1,500 light-years away. At that distance, the above image spans less than 10 light-years.

APOD: 2004 February 5 - NGC 1569: Starburst in a Small Galaxy
Explanation: Grand spiral galaxies often seem to get all the glory, flaunting their young, bright, blue star clusters in beautiful, symmetric spiral arms. But small, irregular galaxies form stars too. In fact, as pictured here, dwarf galaxy NGC 1569 is apparently undergoing a burst of star forming activity, thought to have begun over 25 million years ago. The resulting turbulent environment is fed by supernova explosions as the cosmic detonations spew out material and trigger further star formation. Two massive star clusters - youthful counterparts to globular star clusters in our own spiral Milky Way galaxy - are seen left of center in the gorgeous Hubble Space Telescope image. The picture spans about 1,500 light-years across NGC 1569. A mere 7 million light-years distant, this relatively close starburst galaxy offers astronomers an excellent opportunity to study stellar populations in rapidly evolving galaxies. NGC 1569 lies in the long-necked constellation Camelopardalis.

APOD: 2004 February 3 - X-Rays From Antennae Galaxies
Explanation: A bevy of black holes and neutron stars shine as bright, point-like sources against bubbles of million degree gas in this false-color x-ray image from the orbiting Chandra Observatory. The striking picture spans about 80 thousand light-years across the central regions of two galaxies, NGC 4038 and NGC 4039, locked in a titanic collision some 60 million light-years away in the constellation Corvus. In visible light images, long, luminous, tendril-like structures emanating from the wreckage lend the pair their popular moniker, the Antennae Galaxies. Galactic collisions are now thought to be fairly common, but when they happen individual stars rarely collide. Instead gas and dust clouds merge and compress, triggering furious bursts of massive star formation with thousands of resulting supernovae. The exploding stars litter the scene with bubbles of shocked gas enriched in heavy elements, and collapsed stellar cores. Transfixed by this cosmic accident astronomers watch and are beginning to appreciate the collision-driven evolution of galaxies, not unlike our own.

APOD: 2004 February 2 - The Tarantula Nebula from Spitzer
Explanation: In the heart of monstrous Tarantula Nebula lies one of the most unusual star clusters. Known as NGC 2070 or R136, it is home to a great number of hot young stars. The energetic light from these stars continually ionizes nebula gas, while their energetic particle wind blows bubbles and defines intricate filaments. The new Spitzer Space Telescope took the above representative-color infrared image of this great LMC cluster. The image details the cluster's tumultuous center in gas, dust and young stars. The 30 Doradus nebula is one of the largest star-formation regions known, and has been creating unusually strong episodes of star formation every few million years. In the heart of this heart is a central knot of stars that is so dense it was once thought to be a single star.

APOD: 2003 December 26 - Young Star, Dark Cloud
Explanation: High-speed outflows of molecular gas from a young stellar object glow in infrared light, revealing themselves in this recent false-color image from the Spitzer Space Telescope. Cataloged as HH (Herbig-Haro) 46/47 the infrared source is lodged within a dark nebula or Bok globule - near the lower right corner of the dark nebula in the optical inset - that is largely opaque when viewed in visible light. The energetic outflow features extend for nearly a light-year, burrowing into the dark interstellar material, and are attributed to early stages in the life of a sun-like star. They may well represent a phase of our own Sun's evolution which took place some 4.5 billion years ago, along with the formation of our solar system from a circumstellar disk. A tantalizing object to explore with Spitzer's infrared capabilities, this young star system is relatively nearby, located only some 1,140 light-years distant in the nautical constellation Vela.

APOD: 2003 November 15 - LL Orionis: When Cosmic Winds Collide
Explanation: This arcing, graceful structure is actually a bow shock about half a light-year across, created as the wind from young star LL Orionis collides with the Orion Nebula flow. Adrift in Orion's stellar nursery and still in its formative years, variable star LL Orionis produces a wind more energetic than the wind from our own middle-aged sun. As the fast stellar wind runs into slow moving gas a shock front is formed, analogous to the bow wave of a boat moving through water or a plane traveling at supersonic speed. The slower gas is flowing away from the Orion Nebula's hot central star cluster, the Trapezium, located off the lower right hand edge of the picture. In three dimensions, LL Ori's wrap-around shock front is shaped like a bowl that appears brightest when viewed along the "bottom" edge. The complex stellar nursery in Orion shows a myriad of similar fluid shapes associated with star formation, including the bow shock surrounding a faint star at the upper right. Part of a mosaic covering the Great Nebula in Orion, this composite color image was recorded in 1995 by the Hubble Space Telescope.

APOD: 2003 November 5 - The Lynx Arc
Explanation: While chasing the spectrum of a mysterious arc in a cluster of galaxies within the obscure northerly constellation Lynx, astronomers have stumbled upon the most massive and distant star-forming region ever discovered. The notably red "Lynx arc" lies right of center in this color image of the galaxy cluster, a composite of Hubble Space Telescope and ground-based data. While the galaxy cluster lies about 5 billion light-years distant, spectroscopic studies show that the arc itself is actually a distorted image of an even more distant but enormous star-forming region. The image is formed as the closer galaxy cluster's gravity bends light like a magnifying lens, an effect explained by Einstein's theory of gravity. In fact, the monster star-forming region is nearly 12 billion light-years away and about a million times brighter than the more familiar stellar nursery, the Orion Nebula. Estimates are that the star-forming region seen as the Lynx arc contains about a million massive, hot stars, compared to the four stars which power the Orion Nebula's glow. Stars within the Lynx arc are more than twice as hot as the Orion Nebula's central stars and were formed when the Universe was a mere 2 billion years old. Still, astronomers believe that the first stars were formed at even earlier times.

APOD: 2003 October 19 - An Unusual Globule in IC 1396
Explanation: Is there a monster in IC 1396? Known to some as the Elephant's Trunk Nebula, parts of gas and dust clouds of this star formation region may appear to take on foreboding forms, some nearly human. The only real monster here, however, is a bright young star too far from Earth to hurt us. Energetic light from this star is eating away the dust of the dark cometary globule near the top of the above image. Jets and winds of particles emitted from this star are also pushing away ambient gas and dust. Nearly 3,000 light-years distant, the relatively faint IC 1396 complex covers a much larger region on the sky than shown here, with an apparent width of more than 10 full moons.

APOD: 2003 September 3 - Galactic Supernova Remnant IC 443
Explanation: About 8000 years ago, a star in our Galaxy exploded. Ancient humans might have noticed the supernova as a temporary star, but modern humans can see the expanding shell of gas even today. Pictured above, part of the shell of IC 443 is seen to be composed of complex filaments, some of which are impacting an existing molecular cloud. Here emission from shock-excited molecular hydrogen is allowing astronomers to study how fast moving supernova gas affects star formation in the cloud. Additionally, astronomers theorize that the impact accelerates some particles to velocities near the speed of light. Supernova remnant IC 443 is also known to shine brightly also in infrared and X-ray light.

APOD: 2003 August 30 - Recycling Cassiopeia A
Explanation: For billions of years, massive stars in our Milky Way Galaxy have lived spectacular lives. Collapsing from vast cosmic clouds, their nuclear furnaces ignite and create heavy elements in their cores. After a few million years, the enriched material is blasted back into interstellar space where star formation begins anew. The expanding debris cloud known as Cassiopeia A is an example of this final phase of the stellar life cycle. Light from the explosion which created this supernova remnant was probably first seen in planet Earth's sky just over 300 years ago, although it took that light more than 10,000 years to reach us. In this gorgeous Hubble Space Telescope image of cooling filaments and knots in the Cas A remnant, light from specific elements has been color coded to help astronomers understand the recycling of our galaxy's star stuff. For instance, red regions are dominated by emission from sulfur atoms while blue shades correspond to oxygen. The area shown is about 10 light-years across.

APOD: 2003 August 21 - X-Rays from M17
Explanation: About 5,000 light-years away, toward the constellation Sagittarius and the center of our galaxy, lies the bright star forming region cataloged as M17. In visible light, M17's bowed and hollowed-out appearance has resulted in many popular names like the Horseshoe, Swan, Omega, and Lobster nebula. But what has sculpted this glowing gas cloud? This Chandra Observatory image of x-rays from M17 provides a clue. Many massive young stars are responsible for the pink central region of the false-color x-ray picture, their colliding stellar winds producing the multimillion degree gas cloud which extends ten or so light-years to the left. When compared with visible light images, this x-ray hot cloud is partly surrounded by the nebula's cooler gas. In fact, having carved out a central cavity the hot gas seems to be flowing out of the horseshoe shape like champagne from an uncorked bottle ... suggesting yet another name for star forming region M17.

APOD: 2003 August 16 - Thackeray's Globules
Explanation: Rich star fields and glowing hydrogen gas silhouette dense, opaque clouds of interstellar gas and dust in this Hubble Space Telescope close-up of IC 2944, a bright star forming region in Centaurus, 5,900 light-years away. The largest of these dark globules, first spotted by South African astronomer A. D. Thackeray in 1950, is likely two separate but overlapping clouds, each more than one light-year wide. Combined the clouds contain material equivalent to about 15 times the mass of the Sun, but will they actually collapse to form massive stars? Along with other data, the sharp Hubble images indicate that Thackeray's globules are fractured and churning as a result of intense ultraviolet radiation from young, hot stars already energizing and heating the bright emission nebula. These and similar dark globules known to be associated with other star forming regions may ultimately be dissipated by their hostile environment -- like cosmic lumps of butter in a hot frying pan.

APOD: 2003 August 8 - Blue Stragglers in NGC 6397
Explanation: In our neck of the Galaxy stars are too far apart to be in danger of colliding, but in the dense cores of globular star clusters star collisions may be relatively common. In fact, researchers have evidence that the closely spaced blue stars near the center of the above image taken by the orbiting Hubble Space Telescope were formed when stars directly collided. Pictured is the central region of NGC 6397, a globular cluster about 6,000 light-years distant, whose stars all formed at about the same time. NGC 6397's massive stars have long since evolved off the main sequence, exhausting their central supplies of nuclear fuel. This should leave the cluster with only old low mass stars; faint red main sequence stars and brighter blue and red giants. However, spectroscopic data show that the indicated stars, descriptively dubbed blue stragglers, are clearly main sequence stars which are too blue and too massive to still be there. Suggestively the stragglers appear to be two and occasionally three times as massive as the lower mass cluster stars otherwise present, supporting evidence for their formation from two and even three star collisions.

APOD: 2003 July 18 - The Planet, the White Dwarf, and the Neutron Star
Explanation: A planet, a white dwarf, and a neutron star orbit each other in the giant globular star cluster M4, some 5,600 light-years away. The most visible member of the trio is the white dwarf star, indicated above in an image from the Hubble Space Telescope, while the neutron star is detected at radio frequencies as a pulsar. A third body was known to be present in the pulsar/white dwarf system and a detailed analysis of the Hubble data has indicated it is indeed a planet with about 2.5 times the mass of Jupiter. In such a system, the planet is likely to be about 13 billion years old. Compared to our solar system's tender 4.5 billion years and other identified planets of nearby stars, this truly ancient world is by far the oldest planet known, almost as old as the Universe itself. Its discovery as part of an evolved cosmic trio suggests that planet formation spans the age of the Universe and that this newly discovered planet is likely only one of many formed in the crowded environs of globular star clusters.

APOD: 2003 June 22 - Massive Stars of 30 Doradus
Explanation: In the center of star-forming region 30 Doradus lies a huge cluster of the largest, hottest, most massive stars known. These stars and part of the surrounding nebula are captured here in this gorgeous visible-light Hubble Space Telescope image. Gas and dust clouds in 30 Doradus, also known as the Tarantula Nebula, have been sculpted into elongated shapes by powerful winds and ultraviolet radiation from these hot cluster stars. Insets in the picture represent corresponding views from the Hubble's infrared camera where each square measures 15.5 light-years across. Penetrating the obscuring dust, these infrared images themselves offer detailed pictures of star formation within the nebula's collapsing clouds, revealing the presence of newborn massive stars. The 30 Doradus Nebula lies within a neighboring galaxy, the Large Magellanic Cloud, located a mere 170,000 light-years away.

APOD: 2003 June 20 - Snake in the Dark
Explanation: Dark nebulae snake across a gorgeous expanse of stars in this wide-field view toward the pronounceable constellation Ophiucus and the center of our Milky Way Galaxy. In fact, the central S-shape seen here is well known as the Snake Nebula. It is also listed as Barnard 72 (B72), one of 182 dark markings of the sky cataloged in the early 20th century by astronomer E. E. Barnard. Unlike bright emission nebulae and star clusters, Barnard's nebulae are interstellar dark clouds of obscuring gas and dust. Their shapes are visible in cosmic silhouette only because they lie in the foreground along the line of sight to rich star fields and glowing stellar nurseries near the plane of our Galaxy. Many of Barnard's dark nebulae are themselves likely sites of future star formation. Barnard 72 is a few light years across and about 650 light years away.

APOD: 2003 June 12 - Cyg X-1: Can Black Holes Form in the Dark?
Explanation: The formation of a black hole from the collapsing core of a massive star is thought to be heralded by a spectacular supernova explosion. Such an extremely energetic collapse is also a leading explanation for the mysterious cosmic gamma-ray bursts. But researchers now suggest that the Milky Way's most famous black hole, Cygnus X-1, was born when a massive star collapsed -- without any supernova explosion at all. Their dynamical evidence is summarized in this color image of a gorgeous region in Cygnus, showing Cyg X-1 and a cluster of massive stars (yellow circles) known as Cygnus OB3. Arrows compare the measured direction and speed of Cyg X-1 and the average direction and speed of the massive stars of Cyg OB3. The similar motions indicate that Cyg X-1's progenitor star was itself a cluster member and that its path was not altered at all when it became a black hole. In contrast, if Cyg X-1 were born in a violent supernova it would have likely received a fierce kick, changing its course. If not a supernova, could the formation of the Cyg X-1 black hole have produced a dark gamma-ray burst in the Milky Way?

APOD: 2003 May 3 - Denizen of the Tarantula Nebula
Explanation: The star cluster at lower right, cataloged as Hodge 301, is a denizen of the Tarantula Nebula. An evocative nebula in the southern sky, the sprawling cosmic Tarantula is an energetic star forming region some 168,000 light-years distant in our neighboring galaxy the Large Magellanic Cloud. The stars within Hodge 301 formed together tens of millions of years ago and as the massive ones quickly exhaust their nuclear fuel they explode. In fact, the giant stars of Hodge 301 are rapidly approaching this violent final phase of stellar evolution - known as a supernova. These supernova blasts send material and shock waves back into the nebular gas to create the Tarantula's glowing filaments also visible in this Hubble Space Telescope Heritage image. But these spectacular stellar death explosions signal star birth as well, as the blast waves condense gas and dust to ultimately form the next generation of stars inside the Tarantula Nebula.

APOD: 2003 April 25 - M17: A Hubble Close-Up
Explanation: Sculpted by stellar winds and radiation, these fantastic, undulating shapes lie within the stellar nursery known as M17, the Omega Nebula, some 5,500 light-years away in the nebula-rich constellation Sagittarius. The lumpy features in the dense cold gas and dust are illuminated by stars off the upper left of the image and may themselves represent sites of future star formation. Colors in the fog of surrounding hotter material indicate M17's chemical make up. The predominately green glow corresponds to abundant hydrogen, with trace sulfur and oxygen atoms contributing red and blue hues. The picture spans about 3 light-years and was released to celebrate the thirteenth year of the Hubble Space Telescope's cosmic voyage of exploration.

APOD: 2003 April 23 - The Stars of NGC 1705
Explanation: Some 2,000 light-years across, NGC 1705 is small as galaxies go, similar to our Milky Way's own satellite galaxies, the Magellanic Clouds. At a much larger distance of 17 million light-years, the stars of NGC 1705 are still easily resolved in this beautiful image constructed from data taken in 1999 and 2000 with the Hubble Space Telescope. Most of the younger, hot, blue stars in the galaxy are seen to be concentrated in a large central star cluster with the older, cooler, red stars more evenly distributed. Possibly 13 billion years old, NGC 1705 could well have been forming stars through out its lifetime while light from its most recent burst of star formation reached Earth only 30 million years ago. This gradually evolving dwarf irregular galaxy lacks organized structures like spiral arms and is thought to be a nearby analog to the first galaxies to form in the early Universe.

APOD: 2003 April 7 - NGC 281: Cluster, Clouds, and Globules
Explanation: NGC 281 is a busy workshop of star formation. Prominent features include a small open cluster of stars, a diffuse red-glowing emission nebula, large lanes of obscuring gas and dust, and dense knots of dust and gas in which stars may still be forming. The open cluster of stars IC 1590 visible around the center has formed only in the last few million years. The brightest member of this cluster is actually a multiple-star system shining light that helps ionize the nebula's gas, causing the red glow visible throughout. The lanes of dust visible below the center are likely homes of future star formation. Particularly striking in the above photograph are the dark Bok globules visible against the bright nebula. Stars are surely forming there right now. The entire NGC 281 system lies about 10 thousand light years distant.

APOD: 2003 March 4 - In the Center of the Lagoon Nebula
Explanation: The center of the Lagoon Nebula is busy with the awesome spectacle of star formation. Visible in the lower left, at least two long funnel-shaped clouds, each roughly half a light-year long, have been formed by extreme stellar winds and intense energetic starlight. The tremendously bright nearby star, Hershel 36, lights the area. Vast walls of dust hide and redden other hot young stars. As energy from these stars pours into the cool dust and gas, large temperature differences in adjoining regions can be created generating shearing winds which may cause the funnels. This picture, spanning about 5 light years, was taken in 1995 by the orbiting Hubble Space Telescope. The Lagoon Nebula, also known as M8, lies about 5000 light years distant toward the constellation of Sagittarius.

APOD: 2003 February 8 - AB Aurigae: How To Make Planets
Explanation: This enhanced Hubble Space Telescope image shows in remarkable detail the inner portion of the disk of dust and gas surrounding the star AB Aurigae. Knots of material, visible here for the first time, may well represent an early stage of a process which could result in the formation of planets over the next few million years. AB Aurigae is a young star (2-4 million years old), about 469 light-years distant. Its swirling circumstellar disk is large, about 30 times the size of our solar system. Astronomers believe planet-making is just beginning in AB Aurigae's disk because known disks surrounding younger stars (less than 1 million years old) do not show such clumpy structure, while disks of slightly older stars (aged 8-10 million years) have gaps and features suggesting that planets have already been formed. Why the window pane appearance? Wide black stripes in the picture are caused by occulting bars used to block out the overwhelming starlight. The diagonal streaks are due to diffraction spikes.

APOD: 2003 February 6 - X-Rays from M83
Explanation: Bright and beautiful spiral galaxy M83 lies a mere twelve million light-years from Earth, toward the headstrong constellation Hydra. Sweeping spiral arms, prominent in visible light images, lend this galaxy its popular moniker -- the Southern Pinwheel. In fact, the spiral arms are still apparent in this Chandra Observatory false-color x-ray image of M83, traced by diffuse, hot, x-ray emitting gas. But more striking in the x-ray image is the galaxy's bright central region. The central emission likely represents even hotter gas created by a sudden burst of massive star formation. Point-like neutron star and black hole x-ray sources, final stages in the life cycles of massive stars, also show a concentration near the center of M83 and offer further evidence for a burst of star formation at this galaxy's core. Light from this burst of star formation would have first reached Earth some 20 million years ago.

APOD: 2003 January 27 - BHR 71: Stars, Clouds, and Jets
Explanation: What is happening to molecular cloud BHR 71? Quite possible, a binary star system is forming inside. Most stars in our Galaxy are part of binary star systems, but few have ever been seen in formation. Recent observations of dust-darkened Bok Globule BHR 71, however, show evidence for two young stars forming deep in the cloud, likely close enough to form a binary. Isolated BHR 71 spans about one light year and lies only about 600 light years away in the southern sky. The brighter embedded star -- not visible here -- is about 10 times as bright as the Sun and drives the jet that swept out the empty lane. The above four-color image was taken with a Very Large Telescope in Chile.

APOD: 2002 December 20 - Colorful Clouds of Orion
Explanation: Revisiting one of the most famous nebulae in planet Earth's night sky, astrophotographer Robert Gendler has constructed this stunning, color-enhanced mosaic of the region surrounding the Great Nebula in Orion. As seen here, the clouds of Orion are dominated by the reddish emission nebula M42 near the bottom of the image, with blue reflection nebulae, including NGC 1977, near the top. Strewn with dust lanes and dark nebulae, the striking cosmic apparitions surrounding Orion's stellar nurseries are about 1,500 light-years away and are themselves several light-years across. Located at the edge of a giant molecular cloud complex spanning hundreds of light-years, these nebulae represent only a small, but very visible(!), fraction of this region's wealth of interstellar material. Within these colorful clouds of Orion, astronomers have also identified what appear to be numerous infant solar systems.

APOD: 2002 November 2 - NGC 604: Giant Stellar Nursery
Explanation: Scattered within this cavernous nebula, cataloged as NGC 604, are over 200 newly formed hot, massive, stars. At 1,500 light-years across, this expansive cloud of interstellar gas and dust is effectively a giant stellar nursery located some three million light-years distant in the spiral galaxy, M33. The newborn stars irradiate the gas with energetic ultraviolet light stripping electrons from atoms and producing a characteristic nebular glow. The details of the nebula's structure hold clues to the mysteries of star formation and galaxy evolution.

APOD: 2002 October 17 - Centaurus A: Young Blue Star Stream
Explanation: Almost lost in this cosmic jumble of stars, gas and dust is a faint but definite blue arc -- a stream of young stars whose formation was probably triggered as a small dwarf galaxy was torn apart approaching the giant elliptical galaxy Centaurus A. The 2,000 light-year long arc is revealed in the upper right corner of this processed color digital image, while the dense central region of Centaurus A is near the bottom. Star clusters that make up the blue arc are likely strung out along the incoming trajectory of the small galaxy and are estimated to be only 200-400 million years old. The remarkable result suggests that astronomers have identified a spectacular example of a kind of galactic cannibalism in progress, a process which is believed to contribute to the formation and evolution of large galaxies, including our own Milky Way. Over time, stars and star clusters in this stream should eventually disperse and merge with tumultuous Centaurus A. The image data was recorded with the four meter Blanco telescope at Cerro Tololo Inter-American Observatory.

APOD: 2002 July 25 - NGC 1569: Heavy Elements from a Small Galaxy
Explanation: For astronomers, elements other than hydrogen and helium are sometimes considered to be simply "heavy elements". It's understandable really, because even lumped all together heavy elements make up an exceedingly small fraction of the Universe. Still, heavy elements can profoundly influence galaxy and star formation ... not to mention the formation of planets and people. In this tantalizing false-color x-ray image from the orbiting Chandra Observatory, small dwarf galaxy NGC 1569 is surrounded by x-ray emitting clouds of gas thousands of light-years across. The gas has recently been observed to contain significant concentrations of astronomers' heavy elements such as oxygen, silicon, and magnesium, supporting the idea that dwarf galaxies, the most common type of galaxy in the Universe, are largely responsible for heavy elements in intergalactic space. A mere 7 million light-years distant toward the long-necked constellation Camelopardalis, NGC 1569 has undergone a recent burst of star formation and stellar supernova explosions. The furious cosmic activity has heated the expanding gas clouds to temperatures of millions of degrees while enriching them with newly synthesized heavy elements.

APOD: 2002 July 12 - Recycling Cassiopeia A
Explanation: For billions of years, massive stars in our Milky Way Galaxy have lived spectacular lives. Collapsing from vast cosmic clouds, their nuclear furnaces ignite and create heavy elements in their cores. After a few million years, the enriched material is blasted back into interstellar space where star formation begins anew. The expanding debris cloud known as Cassiopeia A is an example of this final phase of the stellar life cycle. Light from the explosion which created this supernova remnant was probably first seen in planet Earth's sky just over 300 years ago, although it took that light more than 10,000 years to reach us. In this gorgeous Hubble Space Telescope image of cooling filaments and knots in the Cas A remnant, light from specific elements has been color coded to help astronomers understand the recycling of our galaxy's star stuff. For instance, red regions are dominated by emission from sulfur atoms while blue shades correspond to oxygen. The area shown is about 10 light-years across.

APOD: 2002 July 11 - M51: X Rays from the Whirlpool
Explanation: Fresh from yesterday's episode, a popular pair of interacting galaxies known as the Whirlpool debut here beyond the realm of visible light -- imaged at high energies by the orbiting Chandra X-ray Observatory. Still turning in a remarkable performance, over 80 glittering x-ray stars are present in the Chandra image data from the region. The number of luminous x-ray sources, likely neutron star and black hole binary systems within the confines of M51, is unusually high for normal spiral or elliptical galaxies and suggests this cosmic whirlpool has experienced intense bursts of massive star formation. The bright cores of both galaxies, NGC 5194 and NGC 5195 (right and left respectively), also exhibit high-energy activity in this false-color x-ray picture showing a diffuse glow from multi-million degree gas. An expanded view of the region near the core of NGC 5194 reveals x-rays from a supernova remnant, the debris from a spectacular stellar explosion, first detected by earthbound astronomers in 1994.

APOD: 2002 July 4 - Young Star Clusters in an Old Galaxy
Explanation: Elliptical galaxy NGC 4365 is old, probably about 12 billion years old. Like most elliptical galaxies, this galaxy was thought to be full of old stars too, its burst of star forming activity having long since ended. But combining data from the Hubble Space Telescope and the European Southern Observatory's ground-based Antu Telescope, a team of European and US astronomers discovered NGC 4365's surprising secret -- some of its star clusters are young. In this composite image, the galaxy's bright nucleus is at the upper left. NGC 4365's star clusters themselves appear as bright dots against a diffuse glow of unresolved starlight and fuzzy, distant background galaxies. The notched border outlines Hubble's WFPC2 camera field. Moving the cursor over the image identifies individual star clusters, with the relatively young (few billion year-old) clusters circled in blue, and the anticipated 12 billion year-old clusters circled in red. NGC 4365 is 60 million light-years away in the Virgo galaxy cluster.

APOD: 2002 May 3 - Cone Nebula Close Up
Explanation: Cones, pillars, and majestic flowing shapes abound in stellar nurseries where natal clouds of gas and dust are buffeted by energetic winds from newborn stars. A well-known example, the Cone Nebula within the bright galactic star-forming region NGC 2264, was captured in this close-up view from the Hubble Space Telescope's newest camera. While the Cone Nebula, about 2,500 light-years away in Monoceros, is around 7 light-years long, the region pictured here surrounding the cone's blunted head is a mere 2.5 light-years across. In our neck of the galaxy that distance is just over half way from the Sun to its nearest stellar neighbor, Alpha Centauri. The massive star NGC 2264 IRS, seen by Hubble's infrared camera in 1997, is the likely source of the wind sculpting the Cone Nebula and lies off the top of the image. The Cone Nebula's reddish veil is produced by glowing hydrogen gas.

APOD: 2002 March 25 - An Unusual Globule in IC 1396
Explanation: Is there a monster in IC 1396? Known to some as the Elephant's Trunk Nebula, parts of gas and dust clouds of this star formation region may appear to take on foreboding forms, some nearly human. The only real monster here, however, is a bright young star too far from Earth to hurt us. Energetic light from this star is eating away the dust of the dark cometary globule near the top of the above image. Jets and winds of particles emitted from this star are also pushing away ambient gas and dust. Nearly 3,000 light-years distant, the relatively faint IC 1396 complex covers a much larger region on the sky than shown here, with an apparent width of more than 10 full moons.

APOD: 2002 March 13 - LL Orionis: When Cosmic Winds Collide
Explanation: This arcing, graceful structure is actually a bow shock about half a light-year across, created as the wind from young star LL Orionis collides with the Orion Nebula flow. Adrift in Orion's stellar nursery and still in its formative years, variable star LL Orionis produces a wind more energetic than the wind from our own middle-aged sun. As the fast stellar wind runs into slow moving gas a shock front is formed, analogous to the bow wave of a boat moving through water or a plane traveling at supersonic speed. The slower gas is flowing away from the Orion Nebula's hot central star cluster, the Trapezium, located off the lower right hand edge of the picture. In three dimensions, LL Ori's wrap-around shock front is shaped like a bowl that appears brightest when viewed along the "bottom" edge. The complex stellar nursery in Orion shows a myriad of similar fluid shapes associated with star formation, including the bow shock surrounding a faint star at the upper right. Part of a mosaic covering the Great Nebula in Orion, this composite color image was recorded in 1995 by the Hubble Space Telescope.

APOD: 2002 February 18 - A Radio Vista of Cygnus
Explanation: Shells of ancient supernovas, cocoons surrounding newborn stars, and specks from distant quasars highlight this tremendous vista toward the constellation of Cygnus. The representative color image covers about 10 degrees across on the sky but is only a small part of the Canadian Galactic Plane Survey in radio light. Diffuse bands of ionized gas flow though a dominating region of star formation, located about 6000 light-years away. Two prominent supernova shells visible include the brown globule on the lower left and the white bumpy sphere on the upper right. To the left of the brown globule is the entire North America Nebula. Prominent stellar cocoons are visible throughout the image as bright white knots. Some of these stars will likely generate future supernova shells. Far in the distance, visible here as only red dots, quasars glow.

APOD: 2002 January 8 - Thackeray's Globules
Explanation: Rich star fields and glowing hydrogen gas silhouette dense, opaque clouds of interstellar gas and dust in this Hubble Space Telescope close-up of IC 2944, a bright star forming region in Centaurus, 5,900 light-years away. The largest of these dark globules, first spotted by South African astronomer A. D. Thackeray in 1950, is likely two separate but overlapping clouds, each more than one light-year wide. Combined the clouds contain material equivalent to about 15 times the mass of the Sun, but will they actually collapse to form massive stars? Along with other data, the sharp Hubble images indicate that Thackeray's globules are fractured and churning as a result of intense ultraviolet radiation from young, hot stars already energizing and heating the bright emission nebula. These and similar dark globules known to be associated with other star forming regions may ultimately be dissipated by their hostile environment -- like cosmic lumps of butter in a hot frying pan. The chevron shape of the picture outlines the detectors of the Hubble's WFPC2 camera.

APOD: 2002 January 4 - M16: Infrared Star Hunt
Explanation: The head of an interstellar gas and dust cloud is shown here in false-color, a near-infrared view recorded by astronomers hunting for stars within M16's Eagle Nebula. Made famous in a 1995 Hubble image of the 7,000 light-year distant star forming region, the pillar-shaped cloud's surface was seen to be covered with finger-like evaporating gaseous globules (EGGs). The near-infrared image penetrates the obscuring dust cloud's edges. But the cloud's core appears dark and opaque, even at these relatively long wavelengths. Still, this image, made with ESO's Antu telescope, reveals a massive, bright yellow star not directly detected in the visible light Hubble data. This very young star lights up the small bluish nebula with a dark, twisted central stripe, just above it. Below and to its right are several much fainter, less massive stars also not seen in visible light - newborn stars which lie within the Eagle's EGGs. These newborn stars may have already been collapsing, forming from material inside the nebula before the intense radiation from other, nearby, emerging hot stars eroded and sculpted the dramatic pillars and EGGs. In any event, as the dusty clouds are eroded away, stars still forming will be cutoff from their reservoir of star stuff. Further growth and even the development of planetary systems will likely be seriously affected.

APOD: 2001 December 30 - Trifid Pillars and Jets
Explanation: Dust pillars are like interstellar mountains. They survive because they are more dense than their surroundings, but they are being slowly eroded away by a hostile environment. Visible in the above picture is the end of a huge gas and dust pillar in the Trifid Nebula, punctuated by a smaller pillar pointing up and an unusual jet pointing to the left. The pink dots are newly formed low-mass stars. A star near the small pillar's end is slowly being stripped of its accreting gas by radiation from a tremendously brighter star situated off the above picture to the upper right. The jet extends nearly a light-year and would not be visible without external illumination. As gas and dust evaporate from the pillars, the hidden stellar source of this jet will likely be uncovered, possibly over the next 20,000 years.

APOD: 2001 December 25 - Star Forming Region Hubble V
Explanation: How did stars form in the early universe? Astronomers are gaining insight by studying NGC 6822, a nearby galaxy classified as irregular by modern standards but appearing more typical of galaxies billions of years ago. Inspection of NGC 6822 shows several bright star groups, including two dubbed Hubble-X and Hubble-V. Pictured above, the Hubble Space Telescope has resolved Hubble V into the energetic stars that are lighting up the surrounding gas. Each star in the central dense knot of Hubble V shines brighter than 100,000 Suns. The Hubble V gas cloud spans about 200 light years and lies about 1.5 million light-years away toward the constellation Sagittarius.

APOD: 2001 December 22 - Hot Stars in the Southern Milky Way
Explanation: Hot blue stars, red glowing hydrogen gas, and dark, obscuring dust clouds are strewn through this dramatic region of the Milky Way in the southern constellation of Ara (the Altar). About 4,000 light-years from Earth, the stars at the left are young, massive, and energetic. Their intense ultraviolet radiation is eating away at the nearby star forming cloud complex - ionizing the hydrogen gas and producing the characteristic red "hydrogen-alpha" glow. At right, visible within the dark dust nebula, is small cluster of newborn stars. This beautiful color picture is a composite of images made through blue, green, and hydrogen-alpha filters.

APOD: 2001 November 3 - Bright Stars, Dim Galaxy
Explanation: These two clusters of bright, newly formed stars surrounded by a glowing nebula lie 10 million light-years away in the dim, irregular galaxy cataloged as NGC 2366. The Hubble Space Telescope image shows that the youngest cluster, the bottom one at about 2 million years old, is still surrounded by the gas and dust cloud it condensed from, while powerful stellar winds from the stars in the older cluster at the top (4-5 million years old), have begun to clear away its central areas giving the entire nebula an apparent inverted hook shape. Compared to the sun, the stars in these clusters are massive and short lived. The brightest one, near the tip of the hook, is a rare Luminous Blue Variable with 30 to 60 times the mass of the sun - similar to the erruptive Eta Carinae in our own Milky Way. Stars this massive are extremely variable. A comparison with ground based images indicates that in three years this star's brightness increased by about 40 times making it currently the brightest star in this dim galaxy.

APOD: 2001 September 11 - Spiral Galaxy NGC 3310 Across the Visible
Explanation: The party is still going on in spiral galaxy NGC 3310. Roughly 100 million years ago, NGC 3310 likely collided with a smaller galaxy causing the large spiral galaxy to light up with a tremendous burst of star formation. The changing gravity during the collision created density waves that compressed existing clouds of gas and triggered the star-forming party. The above image composite by the Hubble Space Telescope was used to find the ages of many of the resulting clusters of stars. To the surprise of many, some of the clusters are quite young, indicating that starburst galaxies may remain in star-burst mode for quite some time. NGC 3310 spans about 50,000 light years, lies about 50 million light years away, and is visible with a small telescope towards the constellation of Ursa Major.

APOD: 2001 August 29 - AFGL 2591: A Massive Star Acts Up
Explanation: Young star AFGL 2591 is putting on a show. The massive star is expelling outer layers of dust-laced gas as gravity pulls inner material toward the surface. AFGL 2591 is estimated to be about one million years old -- much younger than our own Sun's 5 billion-year age -- and has created a nebula over 500 times the diameter of our Solar System in just the past 10,000 years. The above image in infrared light is one of the first from the new NIRI instrument mounted on one of the largest ground-based optical telescopes in the world: Gemini North. Sharp details are discernable that are blocked by opaque dust in visible-light images. Close inspection of the image reveals at least four expanding rings, indicating an episodic origin to the mysterious activity. AFGL 2591 lies about 3000 light years away toward the constellation of Cygnus.

APOD: 2001 August 22 - The Bubbling Cauldron of NGC 3079
Explanation: Edge-on spiral galaxy NGC 3079 is a mere 50 million light-years away toward the constellation Ursa Major. Shown in this stunning false-color Hubble Space Telescope image, the galaxy's disk - composed of spectacular star clusters in winding spiral arms and dramatic dark lanes of dust - spans some 70,000 light-years. Still, NGC 3079's most eye-catching features are the pillars of gas which tower above a swirling cosmic cauldron of activity at the galaxy's center. Seen in the close-up inset at lower right, the pillars rise to a height of about 2,000 light-years and seem to lie on the surface of an immense bubble rising from the galactic core. Measurements indicate that the gaseous pillars are streaming away from the core at 6 million kilometers per hour. What makes this galaxy's cauldron bubble? Astronomers are exploring the possibility that the superbubble is formed by winds from massive stars. If so, these massive stars were likely born all at once as the galactic center underwent a sudden burst of star formation.

APOD: 2001 July 20 - The Elephant's Trunk in IC 1396
Explanation: Like a picture from a galactic Just So Story, the Elephant's Trunk Nebula winds through the emission nebula and young star cluster complex IC 1396, in the high and far off constellation of Cepheus. Bright swept-back ridges compose the suggestive form, outlining pockets of interstellar dust and gas. Such embedded dark, comet-shaped clouds contain the raw material for star formation. About 3,000 light-years distant, the relatively faint IC 1396 complex covers a much larger region on the sky than shown here, with an apparent width of more than 10 full moons. This close-up telescopic view is a delightful color mosaic of two digital images intended to follow the 'satiable curious cosmic trunk.

APOD: 2001 July 12 - NGC 1850: Not Found in the Milky Way
Explanation: A mere 168,000 light-years distant, this large, lovely cluster of stars, NGC 1850, is located near the outskirts of the central bar structure in our neighboring galaxy, the Large Magellanic Cloud. A first glance at this Hubble Space Telescope composite image suggests that this cluster's size and shape are reminiscent of the ancient globular star clusters which roam our own Milky Way Galaxy's halo. But NGC 1850's stars are young ... making it a type of star cluster with no known counterpart in the Milky Way. NGC 1850 is also a double star cluster, with a second, compact cluster of stars visible here below and to the right of the large cluster's central region. Stars in the large cluster are estimated to be 50 million years young, while stars in the compact cluster are younger still, with an age of about 4 million years. In fact, the smaller cluster contains T-Tauri stars, thought to be low mass, solar-type stars still in the process of formation. The glowing nebula at the left, like the supernova remnants in our own galaxy, testifies to violent stellar explosions, indicating short-lived massive stars were also present in NGC 1850.

APOD: 2001 June 14 - Around The Arches Cluster
Explanation: The most compact cluster of stars known in our galaxy, the Arches cluster, boasts 100 or so massive, young stars contained within a diameter of one light-year. Seen toward the constellation Sagittarius, the Arches cluster is about 25,000 light-years from planet Earth and lies within a scant 100 light-years of the supermassive black hole believed to lurk in our Milky Way Galaxy's center. This combination of images in radio, infrared, and x-ray light illustrates this star cluster's bizarre galactic neighborhood. Shown in red, radio emission traces the filamentary arching structures near the galactic center around the Arches cluster location. Within the zoomed inset box, infrared image data shows some of the cluster's individual stars as bright point-like sources. The diffuse emission in blue surrounding the cluster stars is a false-color x-ray image of an enveloping cloud of 60 million degree gas -- the first time such an energetic star cluster halo has been detected. Astronomers consider the tightly packed and relatively nearby Arches cluster, an analog of the furious star forming regions in galaxies millions of light-years away.

APOD: 2001 June 13 - M94: Beyond the Blue
Explanation: Today's galaxy, M94 (NGC 4736), lies 15 million light-years away in the constellation Canes Venatici. In the red light image (left), its very bright nucleus and tightly wound spiral arms seem to slowly fade into a faint outer disk. But when viewed in wavelengths shorter than blue light - ultraviolet (UV) light - its appearance dramatically changes. While the red light image highlights the older, cooler stars of M94, the UV picture (right), from the shuttle-borne Ultraviolet Imaging Telescope, is dominated by clusters of massive, hot stars a mere 10 million years young. These UV bright young star clusters are mostly arranged in a stunning ring nearly 7,000 light-years wide around the galactic nucleus. What controls this star forming activity? Exploring wavelengths beyond the blue, astronomers now have evidence that star forming activity in galaxies like M94 can be orchestrated by the symmetric structure of the galaxies themselves instead of the titanic galaxy-galaxy collisions suspected in yesterday's case of the Cartwheel galaxy.

APOD: 2001 June 12 - The Cartwheel Galaxy
Explanation: By chance, a collision of two galaxies has created a surprisingly recognizable shape on a cosmic scale. The Cartwheel Galaxy is part of a group of galaxies about 500 million light years away in the constellation Sculptor. Two smaller galaxies in the group are visible on the left of the above photograph. The Cartwheel's rim is an immense ring-like structure 100,000 light years in diameter composed of newly formed, extremely bright, massive stars. When galaxies collide, they pass through each other -- their individual stars rarely come into contact. The galaxies' gravitational fields, however, may be greatly distorted by the collision. In fact, the ring-like shape is the result of the gravitational disruption caused by a small intruder galaxy passing through a large one, compressing the interstellar gas and dust, and causing a wave of star formation wave to move out from the impact point like a ripple across the surface of a pond. In this case, the large galaxy may have originally been a spiral, not unlike our own Milky Way Galaxy, transformed by the collision. Recent astronomical detective work has indicated what has become of the intruder.

APOD: 2001 June 4 - The T Tauri Star Forming System
Explanation: What did the Sun look like before there were planets? A prototype laboratory for the formation of low mass stars like our Sun is the T Tauri system, one of the brighter star systems toward the constellation of Taurus. In young systems, gravity causes a gas cloud to condense. The situation then usually becomes quite complex, as some of the infalling gas is heated so much by collisions that it is immediately expelled as an outgoing wind. Complex geometries including jets and disks form as the infalling and outflowing gas collide and interact with a changing magnetic field. Pictured above is a false-color image of the T Tauri system itself, which turns out to be a binary. In a few million years, the central condensate will likely become hot enough to ignite nuclear fusion, by which time much of the surrounding circumstellar material will either have fallen in or have been driven off by the stellar wind. At that time, a new star will shine.

APOD: 2001 May 18 - HD 82943: Planet Swallower
Explanation: Stars like HD 82943 are main sequence G dwarf stars with temperatures and compositions similar to the Sun. Also like the Sun, HD 82943 is known to have at least two giant planets, but unlike gas giants in our solar system their orbits are not nearly circular and bring them closer to the parent star. Astronomers now point to strong observational evidence that HD 82943 used to have more planets ... but swallowed them in the past. Such a cosmic cataclysm is illustrated above in an artist's dramatic vision. As a result, planetary debris would contaminate the outer layers of HD 82943. Researchers using a high resolution spectrograph at the European Southern Observatory's Kueyen telescope believe they have seen a clear signature of this contamination by identifying the isotope Lithium-6 in this sun-like star's spectrum. Because the light element Lithium-6 is so readily destroyed in nuclear reactions during star formation, no significant Lithium-6 should now exist in HD 82943. Startlingly, perhaps the most likely explanation for the presence of Lithium-6 today is that it is left over from planetary material which formed separately and was then absorbed by the parent star.

APOD: 2001 May 4 - Protoplanetary Survivors in Orion
Explanation: The Orion Nebula is a nuturing stellar nursery filled with hot young stars and their natal clouds of gas and dust. But for planetary systems, the active star-forming region can present a hazardous and inhospitable birthplace. While the formation of dusty protoplanetary disks seems common in Orion, these Hubble Space Telescope close-up images dramatically reveal the torturous conditions they must face while trying to grow into full-fledged planetary systems. In each case, a central young star is surrounded by a disk substantially wider than our solar system. The disks likely contain material in the process of planet formation. However, withering ultraviolet radiation from one of Orion's nearby hot stars is rapidly destroying the disks -- ultimately creating the comet-shaped clouds of glowing gas seen engulfing the protoplanetary systems. Planet formation must occur quickly here, if at all. Researchers estimate that about 90 percent of Orion's youngest protoplanetary disks will not survive the next 100,000 years.

APOD: 2001 April 13 - GRB010222: Gamma Ray Burst, X Ray Afterglow
Explanation: A fading afterglow from one of the most powerful explosions in the universe is centered in this false color image from the spacebased Chandra X-ray Observatory. The cosmic explosion, an enormously bright gamma-ray burst (GRB), originated in a galaxy billions of light-years away and was detected by the BeppoSAX satellite on February 22. GRB010222 was visible for only a few seconds at gamma-ray energies, but its afterglow was followed for days by x-ray, optical, infrared and radio instruments. These Chandra observations of the GRB's x-ray glow hours after the initial explosion suggest an expanding fireball of material moving at near light speed has hit a wall of relatively dense gas. While the true nature of gamma-ray bursters remains unknown, the mounting evidence from GRB afterglows does indicate that the cosmic blasts may be hypernovae -- the death explosions of very massive, short-lived stars embedded in active star forming regions. As the hypernova blasts sweep up dense clouds of material in the crowded star forming regions they may also trigger more star formation.

APOD: 2001 March 24 - The UV SMC from UIT
Explanation: Translated from the "acronese" the title reads - The UltraViolet Small Magellanic Cloud from the Ultraviolet Imaging Telescope. FYI, the four ultraviolet images used in this mosaic of the nearby irregular galaxy known as the Small Magellanic Cloud were taken by the UIT instrument during the Astro-1 and Astro-2 shuttle missions in 1990 and 1995. Each separate image field is slightly wider than the apparent size of the full moon. These ultraviolet pictures, shown in false color, must be taken above the Earth's absorbing atmosphere. They highlight concentrations of hot, newly formed stars only a few millions of years old, and reveal the progress of recent star formation in the SMC.

APOD: 2001 March 21 - Barred Spiral Galaxy NGC 2903
Explanation: NGC 2903 is a spiral galaxy similar to our own Milky Way Galaxy. Similarities include its general size and a central bar. One striking difference, however, is the appearance of mysterious hot spots in NGC 2903's core. Upon inspection of the above image and similar images taken by the Hubble Space Telescope, these hot spots were found to be bright young globular clusters, in contrast to the uniformly old globular clusters found in our Milky Way Galaxy. Further investigation has indicated that current star formation is most rampant in a 2000 light-year wide circumnuclear ring surrounding NGC 2903's center. Astronomers hypothesize that the gravity of the central bar expedites star formation in this ring. NGC 2903 lies about 25 million light-years away and is visible with a small telescope towards the constellation of Leo.

APOD: 2001 March 2 - LkHa101: The Hole in the Doughnut
Explanation: You'd need a really big cup of coffee with this doughnut ... because the hole in the middle is about a billion kilometers across. Centered on the Sun, a circle that size would lie between the orbits of Mars and Jupiter. In fact, this doughnut is known to surround a massive newborn star cataloged as LkHa 101 which lies in the constellation Perseus. Imaged in infrared light, the tantalizing torus-shaped cloud of gas and dust is slightly tilted to our view. The cloud's material may well be the ingredients for the formation of a distant solar system. A bright source of ultraviolet light, the hot young star itself is much fainter in the infrared and so not visible in this picture. Still, the star's presence is indicated as its intense stellar wind and radiation has apparently carved out the doughnut's hole. This premier close-up of a stellar system in formation was accomplished by adapting a powerful observational technique called interferometry to planet Earth's largest single mirror telescope, the 10 meter Keck.

APOD: 2001 February 16 - Star Forming Region Hubble X
Explanation: In nearby galaxy NGC 6822, this glowing emission nebula complex surrounds bright, massive, newborn stars. A mere 4 million years young, these stars condensed from the galaxy's interstellar gas and dust clouds. The nebular glow is powered by the bright stars' intense ultraviolet radiation while its shape is sculpted by the interaction of stellar winds and radiation with the immense interstellar clouds themselves. Cataloged as Hubble-X, many skygazers find the appearance of this extragalactic star forming region reminiscent of the most famous stellar nursery in our own galaxy, the Orion Nebula. Hubble-X is intrinsically much brighter than Orion though, and at a distance of 1.6 million light-years it is about 1,000 times farther away. Hubble-X is also about 100 light-years across compared to 10 light-years for the Orion Nebula. Why is it called Hubble-X? X is the Roman numeral 10, this nebula's designation in a catalog of similar objects for galaxy NGC 6822.

APOD: 2001 January 24 - NGC 3603: X-Rays From A Starburst Cluster
Explanation: A mere 20,000 light-years from the Sun lies the NGC 3603 star cluster, a resident of the nearby Carina spiral arm of our Milky Way galaxy. Seen here in this recent false-color x-ray image from the Chandra Observatory, NGC 3603 is well known to astronomers as a young cluster in a large galactic star-forming region. The image colors were chosen to show the relative x-ray brightness of the many individual sources present, where green are faint and red to purple hues are bright sources of x-rays. The stars in the cluster were formed in a single "burst" of star formation only one or two million years ago, so the x-rays are believed to come from the massive young stars themselves or from their energetic stellar winds. Since other common galactic sources of x-rays such as supernova remnants and neutron stars represent final stages in the life of a massive star, they are unlikely to be present in such a young cluster. Nearby NGC 3603 is thought to be a convenient example of the star clusters that populate distant starburst galaxies.

APOD: 2001 January 12 - NGC 1410/1409: Intergalactic Pipeline
Explanation: These two galaxies are interacting in a surprising way, connected by a "pipeline" of obscuring material that runs between them over 20,000 light-years of intergalactic space. Silhouetted by starlight, the dark, dusty ribbon appears to stretch from NGC 1410 (the galaxy at the left) and wrap itself around NGC 1409 (at right). A mere 300 million light-years distant in the constellation of Taurus, the pair's recent collision has likely drawn out this relatively thin lane of material which is only about 500 light-years wide. Though the Hubble Space Telescope image dramatically illustrates how galaxies exchange matter when they collide, it also presents challenges to current pictures of galaxy evolution. The titanic collision has triggered star formation in NGC 1410 as evidenced by its blue star forming regions, yet NGC 1409 remains devoid of hot, young blue stars even though observations indicate that material is flowing into it. Bound by gravity, these two galaxies are doomed to future collisions, merging over time into one.

APOD: 2000 September 24 - M16: Stars from Eagle's Eggs
Explanation: Newborn stars are forming in the Eagle Nebula. This image, taken with the Hubble Space Telescope in 1995, shows evaporating gaseous globules (EGGs) emerging from pillars of molecular hydrogen gas and dust. The giant pillars are light years in length and are so dense that interior gas contracts gravitationally to form stars. At each pillars' end, the intense radiation of bright young stars causes low density material to boil away, leaving stellar nurseries of dense EGGs exposed. The Eagle Nebula, associated with the open star cluster M16, lies about 7000 light years away.

APOD: 2000 September 19 - M17: Omega Nebula Star Factory
Explanation: In the depths of the dark clouds of dust and molecular gas known as M17, stars continue to form. Visible in the above recently released representative-color photograph of M17 by the New Technology Telescope are clouds so dark that they appear almost empty of near infrared light. The darkness of these molecular clouds results from background starlight being absorbed by thick carbon-based smoke-sized dust. As bright massive stars form, they produce intense and energetic light that slowly boils away the dark shroud. M17's unusual appearance has garnered it such nicknames as the Omega Nebula, the Horseshoe Nebula, and the Swan Nebula. M17, visible with binoculars towards the constellation of Sagittarius, lies 5000 light-years away and spans 20 light-years across.

APOD: 2000 August 18 - X-Rays From Antennae Galaxies
Explanation: A bevy of black holes and neutron stars shine as bright, point-like sources against bubbles of million degree gas in this false-color x-ray image from the orbiting Chandra Observatory. The striking picture shows the central regions of two galaxies, NGC 4038 and NGC 4039, locked in a titanic collision some 60 million light-years distant in the constellation Corvus. In visible light images, long, luminous, tendril-like structures emanating from the wreckage lend the pair their popular moniker, the Antennae Galaxies. Galactic collisions are now thought to be fairly common, but when they happen individual stars rarely collide. Instead gas and dust clouds merge and compress, triggering furious bursts of massive star formation with thousands of resulting supernovae. The exploding stars litter the scene with bubbles of shocked hot gas and collapsed stellar cores. Transfixed by this cosmic accident astronomers watch and are beginning to appreciate the collision-driven evolution of galaxies, not unlike our own.

APOD: 2000 July 29 - NGC1850: Star Cluster in the LMC
Explanation: NGC1850 is a large cluster of stars located a mere 166,000 light-years from Earth in our neighboring galaxy the Large Magellanic Cloud (LMC). The colors in this beautiful Hubble Space Telescope composite image of the cluster reveal different populations of stars. Yellowish stars are the main cluster stars, sun-like main sequence hydrogen burners about 50 million years old. The white stars are massive, hotter, and younger, about 4 million years old. Radiating strongly in ultraviolet light, they represent a loose cluster themselves, perhaps within 200 light-years of the main cluster. Massive stars which formed in the older main cluster have long since disappeared, ending their lives in spectacular supernova explosions. Did expanding debris from these supernovae trigger the formation of the nearby younger cluster? Probably so. In any event, a few million years from now a similar fate awaits the massive stars of the younger cluster - burning brightly but briefly before they explode sending new clouds of stellar debris into space.

APOD: 2000 June 22 - Blue Stragglers In NGC 6397
Explanation: In our neck of the Galaxy stars are too far apart to be in danger of colliding, but in the dense cores of globular star clusters star collisions may be relatively common. In fact, researchers have evidence that the row of six closely spaced blue stars just below the label in this Hubble Space Telescope image were formed when stars directly collided. Pictured is the central region of NGC 6397, a globular cluster about 6,000 light-years distant, whose stars all formed at about the same time. NGC 6397's massive stars have long since evolved off the main sequence, exhausting their central supplies of nuclear fuel. This should leave the cluster with only old low mass stars; faint red main sequence stars and brighter blue and red giants. However, spectroscopic data show that the indicated stars, descriptively dubbed blue stragglers, are clearly main sequence stars which are too blue and too massive to still be there. Suggestively the stragglers appear to be two and occasionally three times as massive as the lower mass cluster stars otherwise present, supporting evidence for their formation from two and even three star collisions.

APOD: 2000 May 6 - The Heart Of Orion
Explanation: Newborn stars lie at at the heart of the the Orion Nebula, hidden from view by the dust and gas of the giant Orion Molecular Cloud number 1 (OMC-1). Sensitive to invisible infrared wavelengths, Hubble's NICMOS camera can explore the interior of OMC-1 detecting the infrared radiation from infant star clusters and the interstellar dust and atoms energized by their intense starlight. In this false color picture, stars and the glowing dust clouds which also scatter the starlight appear yellowish orange while emission from hydrogen gas is blue. The dramatic image reveals a wealth of details, including many filaments and arcs of gas and dust -- evidence of violent motions stirred-up by the emerging stars. The bright object near the center is the massive young star "BN" (named for its discoverers Becklin and Neugebauer). The pattern of speckles and ripples surrounding BN and other bright stars are image artifacts.

APOD: 2000 April 21 - M82: Starburst in X-rays
Explanation: Star formation occurs at a faster pace in M82 -- a galaxy with about 10 times the rate of massive star birth (and death) compared to our Milky Way. Winds from massive stars and blasts from supernova explosions have created the expanding cloud of million degree gas filling the above Chandra X-ray Observatory image of this remarkable starburst galaxy. The false color image even resolves bright spots which are likely shocked supernova remnants and X-ray bright binary stars. Also observed as a radio galaxy and a bright celestial infrared source, M82's aspect in optical pictures has led to its popular moniker, the Cigar Galaxy. M82's burst of star formation was likely triggered a mere 100 million years ago in the latest of a series of bouts with another large galaxy, M81.

APOD: 2000 March 31 - Free Floating Planets In Orion
Explanation: This false-colour image of the young Trapezium star cluster in the Orion Nebula was made with an infrared camera at wavelengths about twice as long as visible light. The infrared data are part of a sensitive survey of this nearby star forming region in which astronomers have identified over 100 extremely low mass objects -- candidates for elusive brown dwarf stars. Brown dwarfs are failed stars with masses so low (about 8% of the Sun's) that they can not sustain nuclear hydrogen burning, a sun-like star's main energy source. While brown dwarfs are thought to be still massive enough to burn deuterium for energy, thirteen of the low mass objects show evidence of lying below even the deuterium burning limit (about 1.3% of the Sun's mass) falling in a range more commensurate with giant planets. These drifting, "free-floating planets" are perhaps as little as 8 times as massive as Jupiter and likely formed along with the cluster stars a million or so years ago. They are detectable in the infrared because they are still hot from formation, but will eventually cool and fade. If the Trapezium is typical of young star clusters, then the survey results suggest that brown dwarfs and free-floating planets may be fairly common, but there are not enough to solve the mystery of dark matter in the Universe.

APOD: 2000 March 13 - A Panorama of Oddities in Orion A
Explanation: New stars, fast jets, and shocked gas clouds all occupy Orion A, a giant molecular cloud just south of the Orion Nebula. The bright object visible below and slightly left of center of this recently released picture is the reflection nebula NGC 1999. Wind from NGC 1999's central star, V380 Orionis, appears to have created the surrounding billows of red and brown gas. Several bright young stars illuminate reflecting dust at the top right of the image. Jets shoot from dozens of young stars creating glowing compressed shocked waves known Herbig-Haro objects. One such shock is the unusual Waterfall, the bright streak on the upper right, which is a source of unusual radio waves. The cone-shaped shock to the Waterfall's lower right may result from a jet emitted HH1 and HH2, located 10 light-years away below NGC 1999. The unusual and energetic oddities that occur and interact in star forming regions are often as complex as they are beautiful.

APOD: 2000 February 19 - Young Suns
Explanation: The star cataloged as NGC2264 IRS is normally hidden from the inquiring gaze of optical telescopes. It resides in the midst of the obscuring gas and dust of a nearby star forming region popularly known as the Cone Nebula. Imaged in penetrating infrared light by the Hubble Space Telescope's NICMOS instrument, this young and massive star was found to be surrounded by six "baby" sun-like stars - all within less than a tenth of a light-year of their "big brother". The diffraction spikes and rings surrounding big brother are image artifacts. Astronomers believe that the high speed winds generated by the massive star compressed nearby material causing the formation of the smaller stars in a text book example of triggered star formation. The young suns appear to lie along an otherwise invisible boundary where the high speed gas has collided with the wall of a denser molecular cloud. NGC2264 IRS also seems to be the source of the outflow which created the striking cone shape of the optical nebula.

APOD: 2000 January 7 - NGC 4214: Star Forming Galaxy
Explanation: Dazzling displays of star formation abound across the face of galaxy NGC 4214, a mere 13 million light-years away in the northern constellation Canes Venatici. While this 1997 Hubble Space Telescope image shows the numerous faint, older stars of NGC 4214, the most eye-catching features are the galaxy's bright young star clusters surrounded by fluorescent gas clouds. Sculpted into bubbles and filamentary shapes by energetic explosions and stellar winds from massive cluster stars, the clouds fluoresce in the intense stellar ultraviolet radiation. The colorful spectacle of massive young star forming clusters and distinguished presence of a fainter, older stellar population indicate that NGC 4214 has experienced star formation episodes spanning billions of years.

APOD: October 27, 1999 - In the Heart of the Tarantula Nebula
Explanation: In the heart of monstrous Tarantula Nebula lies one of the most unusual star clusters. Known as NGC 2070 or R136, it is home to a great number of hot young stars. The energetic light from these stars continually ionizes nebula gas, while their energetic particle wind blows bubbles and defines intricate filaments. The above representative-color picture of this great LMC cluster details its tumultuous center in gas, dust and young stars. The 30 Doradus nebula is one of the largest star-formation regions known, and has been creating unusually strong episodes of star formation every few million years. In the heart of this heart is a central knot of stars that is so dense it was once thought to be a single star.

APOD: October 18, 1999 - NGC 3603: An Active Star Cluster
Explanation: NGC 3603 is home to a massive star cluster, thick dust pillars, and a star about to explode. The central open cluster contains about 2000 bright stars, each of which is much brighter and more massive than our Sun. Together, radiations from these stars are energizing and pushing away surrounding material, making NGC 3603 one of the most interesting HII regions known. NGC 3603 is about 20,000 light-years away, and the region shown is about 20 light-years across. Possibly most interesting about this recently released, representative-color picture are the large number of dim stars visible. These stars are less massive than our Sun, demonstrating that great numbers of low-mass stars also form in active starburst regions.

APOD: October 8, 1999 - NGC 1365: Barred Spiral Galaxy
Explanation: NGC 1365 is a giant barred spiral galaxy about 200,000 light-years in diameter and 60 million light-years distant in the southern constellation Fornax. These three recently released images offer views of this majestic island universe in visible and infrared light. In the middle is an optical ground-based image showing NGC 1365's dramatic spiral arms trailing away from its central galactic bar. Superposed colored rectangles define the corresponding fields of the inset images. At upper left, a Hubble Space Telescope near visible light image shows young blue star clusters and dark dust lanes located near the center of NGC 1365. The bright yellow nucleus likely houses a massive black hole. At lower right, the Hubble infrared view of the galaxy's center also shows young star clusters as bright blue spots but additionally reveals infrared-bright spots corresponding to newborn clusters still hidden from optical view by dust clouds. Astronomers believe the gravity field of NGC 1365's bar plays a crucial role in the galaxy's evolution, funneling gas and dust into the central star-forming maelstrom and ultimately feeding material into its massive black hole.

APOD: October 1, 1999 - New Stars In 30 Doradus
Explanation: Compare these matched Hubble Space Telescope views (visible-light on top; infrared on bottom) of a region in the star-forming 30 Doradus Nebula. Find the numbered arrows in the infrared image which identify newborn massive stars. For example, arrows 1 and 5 both point to compact clusters of bright young stars. Formed within collapsing gas and dust clouds, the winds and radiation from these hot stars have cleared away the remaining obscuring material making the clusters easily apparent in both visible and infrared images. But still shrouded in dust and readily seen only in the penetrating infrared view are newborn stars and star systems indicated by arrows 2, 3, and 4. Perhaps even more remarkable are the infrared bright spots indicated by arrows 6 and 7. Exactly in a line on opposite sides of the bright cluster at arrow 5, they may actually be caused by symmetric jets of material produced by one of the young cluster stars. These luminous spots are each about 5 light-years from the cluster and would correspond to points at which the energetic jet material impacts the surrounding dust clouds.

APOD: September 30, 1999 - Massive Stars Of 30 Doradus
Explanation: This gorgeous visible-light Hubble Space Telescope image shows a young cluster of massive stars at the center of the 30 Doradus Nebula. Gas and dust clouds in 30 Doradus, also known as the Tarantula Nebula, have been sculpted into elongated shapes by powerful winds and ultraviolet radiation from these hot cluster stars. Insets in the picture represent corresponding views from the Hubble's infrared camera where each square measures 15.5 light-years across. Penetrating the obscuring dust, these infrared images themselves offer detailed pictures of star formation within the nebula's collapsing clouds, revealing the presence of newborn massive stars. The 30 Doradus Nebula lies within a neighboring galaxy, the Large Magellanic Cloud, located a mere 170,000 light-years away.

APOD: September 24, 1999 - Cometary Globules In Orion
Explanation: Intense ultraviolet light from massive, hot stars in the Orion region has sculpted and compressed clouds of dust and gas in to distinctively shaped Cometary Globules. Seen in this IRAS infrared image recorded at a wavelength sensitive to emission from dust, the elongated globules are easily visible along with a bright region which corresponds to the Trapezium star cluster. Otherwise known as the Witch Head Nebula, IC 2118 is the string of globules near the middle right. Suggestively similar to comets in general appearance only, Cometary Globules are interstellar condensations on a vastly different scale. These are likely related to star formation episodes in the Orion molecular cloud. Besides those indicated by the arrows, more comet-shaped clouds or globules are present in this image.

APOD: August 21, 1999 - Galaxies Away
Explanation: This striking pair of galaxies is far, far away ... about 350 million light-years from Earth. Cataloged as AM0500-620, the pair is located in the southern constellation Dorado. The background elliptical and foreground spiral galaxy are representative of two of the three major classes of galaxies which inhabit our Universe. Within the disks of spiral galaxies, like our own Milky Way, gas, dust, and young blue star clusters trace out grand spiral "arms". The dust lanes along the arms of this particular spiral stand out dramatically in this Hubble Space Telescope image as they obligingly sweep in front of the background elliptical. Like the central bulges of spiral galaxies, elliptical galaxies tend toward spherical shapes resulting from more random motions of their stars. But while spirals produce new stars, star formation in ellipticals which lack gas and dust seems to have stopped. How do galaxies evolve with cosmic time? Evidence is growing that graceful galaxy shapes can hide a violent history.

APOD: July 29, 1999 - Hydrogen Blob N88A in the Small Magellanic Cloud
Explanation: The bright blob of hydrogen gas cataloged as N88A is seen at the right. It measures a mere 3 light years across. Emerging from the cool, dusty interstellar medium in a nearby irregular galaxy known as the Small Magellanic Cloud, N88A hides hot young stars at its core. The false-color Hubble Space Telescope image was recorded in the characteristic "H-alpha" light emitted by hydrogen atoms as they are ionized by the young star's energetic ultraviolet light and then recombine. Other regions of ionized hydrogen (H II regions) which surround new born stars can be over a thousand light-years across but astronomers now recognize that these small ionized hydrogen blobs contain some of the most massive stars known.

APOD: July 21, 1999 - Galactic Supernova Remnant IC 443
Explanation: About 8000 years ago, a star in our Galaxy exploded. Ancient humans might have noticed the supernova as a temporary star, but modern humans can see the expanding shell of gas even today. In the above false-color infrared image of supernova remnant IC 443, blue denotes expanding gas where emission is dominated by excited iron atoms. Of particular interest, though, are the wisps of IC 443 colored red, as they are impacting an otherwise normal molecular cloud. Here emission from shock-excited molecular hydrogen is allowing astronomers to study how fast moving supernova gas affects star formation in the cloud. Additionally, astronomers theorize that the impact accelerates some particles to velocities near the speed of light. The horizontal line across the image is not part of the nebula.

APOD: June 11, 1999 - AB Aurigae: How To Make Planets
Explanation: This enhanced Hubble Space Telescope image shows in remarkable detail the inner portion of the disk of dust and gas surrounding the star AB Aurigae. Knots of material, visible here for the first time, may well represent an early stage of a process which could result in the formation of planets over the next few million years. AB Aurigae is a young star (2-4 million years old), about 469 light-years distant. Its swirling circumstellar disk is large, about 30 times the size of our solar system. Astronomers believe planet-making is just beginning in AB Aurigae's disk because known disks surrounding younger stars (less than 1 million years old) do not show such clumpy structure, while disks of slightly older stars (aged 8-10 million years) have gaps and features suggesting that planets have already been formed. Why the window pane appearance? Wide black stripes in the picture are caused by occulting bars used to block out the overwhelming starlight and the diagonal streaks are due to diffraction spikes.

APOD: June 4, 1999 - NGC 3603: From Beginning To End
Explanation: From beginning to end, different stages of a star's life appear in this exciting Hubble Space Telescope picture of the environs of galactic emission nebula NGC 3603. For the beginning, eye-catching "pillars" of glowing hydrogen at the right signal newborn stars emerging from their dense, gaseous, nurseries. Less noticeable, dark clouds or "Bok globules" at the top right corner are likely part of a still earlier stage, prior to their collapse to form stars. At picture center lies a cluster of bright hot blue stars whose strong winds and ultraviolet radiation have cleared away nearby material. Massive and young, they will soon exhaust their nuclear fuel. Nearing the end of its life, the bright supergiant star Sher 25 is seen above and left of the cluster, surrounded by a glowing ring and flanked by ejected blobs of gas. The ring structure is reminiscent of Supernova 1987a and Sher 25 itself may be only a few thousand years from its own devastating finale. But what about planets? Check out the two teardrop-shaped objects below the cluster toward the bottom of the picture. Although larger, these emission nebulae are similar to suspected proto-planetary disks (proplyds) encompassing stars in the Orion Nebula.

APOD: May 7, 1999 - Hot Stars in the Southern Milky Way
Explanation: Hot blue stars, red glowing hydrogen gas, and dark, obscuring dust clouds are strewn through this dramatic region of the Milky Way in the southern constellation of Ara (the Altar). About 4,000 light-years from Earth, the stars at the left are young, massive, and energetic. Their intense ultraviolet radiation is eating away at the nearby star forming cloud complex - ionizing the hydrogen gas and producing the characteristic red "hydrogen-alpha" glow. At right, visible within the dark dust nebula, is small cluster of newborn stars. This beautiful color picture is a composite of images made through blue, green, and hydrogen-alpha filters.

APOD: April 7, 1999 - Denizen of the Tarantula Nebula
Explanation: The star cluster at lower right, cataloged as Hodge 301, is a denizen of the Tarantula Nebula. An evocative nebula in the southern sky, the sprawling cosmic Tarantula is an energetic star forming region some 168,000 light-years distant in our neighboring galaxy the Large Magellanic Cloud. The stars within Hodge 301 formed together tens of millions of years ago and as the massive ones quickly exhaust their nuclear fuel they explode. In fact, the red giant stars of Hodge 301 are rapidly approaching this violent final phase of stellar evolution - known as a supernova. These supernova blasts send material and shock waves back into the nebular gas to create the Tarantula's glowing filaments also visible in this Hubble Space Telescope Heritage image. But these spectacular stellar death explosions signal star birth as well, as the blast waves condense gas and dust to ultimately form the next generation of stars inside the Tarantula Nebula.

APOD: April 2, 1999 - Stars of NGC 206
Explanation: Nestled within the dusty arms of the large spiral galaxy Andromeda (M31), the star cluster NGC 206 is one of the largest star forming regions known in our local group of galaxies. The beautiful bright blue stars of NGC 206 betray its youth - but close, systematic studies of variable stars in and around NGC 206 will also accurately reveal its distance. Astronomers are searching for variable stars in NGC 206, particularly pulsating stars known as Cepheids and eclipsing binary star systems. Distances for these types of stars can be effectively determined by following the periodic changes in their brightness and spectra. About 3 million light-years away, an accurately known distance to NGC 206 and thus M31 is critical to the larger understanding of galaxy formation, galaxy evolution, and ultimately the distance scale of the Universe.

APOD: November 3, 1998 - Sextans A: A Seemingly Square Galaxy
Explanation: What's bothering local galaxy Sextans A? A small dwarf irregular galaxy spanning 5 thousand light years across, Sextans A is located only 5 million light-years away. Named for its home constellation of Sextans, the "diamond in the rough" structure relates to an ancient unknown event. 100 million years ago, something mysterious started a new wave of star formation in Sextans A's center. Massive short-lived stars exploded in supernovae that caused more star formation and yet more supernovae, ultimately resulting in an expanding shell. Today, young blue stars highlight areas and shell edges high in current star formation, a shell that from our perspective appears roughly square. In the above picture, a bright orange star in our own Milky Way Galaxy appears superposed in the foreground.

APOD: September 21, 1998 - NGC 281: Cluster, Clouds, and Globules
Explanation: NGC 281 is a busy workshop of star formation. Prominent features include a small open cluster of stars, a diffuse red-glowing emission nebula, large lanes of obscuring gas and dust, and dense knots of dust and gas in which stars may still be forming. The open cluster of stars IC 1590 visible on the upper right has formed only in the last few million years. The brightest member of this cluster is actually a multiple-star system shining light that helps ionize the nebula's gas, causing the red glow visible throughout. The lanes of dust on the lower right might be the home of future star formation. Particularly striking in the above photograph are the dark Bok globules visible against the bright nebula. Stars are probably forming there right now. The entire NGC 281 system lies about 10 thousand light years distant.

APOD: July 10, 1998 - Interacting Galaxies
Explanation: This dramatic image of an interacting pair of galaxies was made using the 1.5 meter telescope at the Cerro Tololo Inter-American Observatory near La Serena, Chile. NGC 1531 is the background galaxy with a bright core just above center and NGC 1532 is the foreground spiral galaxy laced with dust lanes. The pair is about 70 million light-years away in the southern constellation Eridanus. These galaxies lie close enough together so that each feels the influence of the other's gravity. The gravitational tug-of-war has triggered star formation in the foreground spiral as evidenced by the young, bright blue star clusters along the edge of the front spiral arm. Though the spiral galaxy in this pair is viewed nearly edge-on, astronomers believe the system is similar to the face-on spiral and companion known as M51, the Whirlpool Galaxy.

APOD: July 1, 1998 - NGC 1808: A Nearby Starburst Galaxy
Explanation: NGC 1808 is a galaxy in turmoil. A barred spiral with marked similarities to our home Milky Way Galaxy, NGC 1808 is distinguished by a peculiar nucleus, an unusually warped disk, and strange flows of hydrogen gas out from the central regions. Amidst all of this, NGC 1808 is undergoing so much star formation it has been deemed a starburst galaxy. In the above color-enhanced photograph, regions of active star formation and shown by their blue glow. Here bright blue stars have recently formed and are energizing large clouds of surrounding hydrogen gas. The reddish brown regions indicate dense interstellar dust. NGC 1808 is a relatively close 40 million light-years away, and stretches about 35,000 light-years across. The peculiar state of NGC 1808 may be caused by the gravity of neighboring galaxy NGC 1792.

APOD: May 29, 1998 - An Extrasolar Planet?
Explanation: This infrared Hubble Space Telescope view may contain the first ever direct image of a planet outside our own solar system. The picture shows a very young double star located about 450 light-years away toward the constellation of Taurus. Cataloged as TMR-1 (Taurus Molecular Ring star 1), the binary system is still embedded in the dust cloud that formed it. This double star and dust cloud are the brightest grouping in the picture, glowing strongly at infrared wavelengths. A filament extends from the binary system toward the lower left and points toward the spot of light representing the candidate planet. Astronomers believe this planet is a "runaway" object which was gravitationally ejected, the filament tracing the path to its present location at about 1500 times the Earth-Sun distance from the parent star system. Models suggest that the planet and binary system are a mere 300,000 years old, with the planet having a mass of about 2 to 3 Jupiters. Future observations to look for the planet's continued runaway motion and spectral signatures should be able to confirm the nature of this object. While this and other tantalizing discoveries of extrasolar planetary objects and protoplanetary disks don't seem to offer direct examples of solar systems like our own, they do strongly hint that planet formation is a varied and common process.

APOD: April 23, 1998 - Three Dusty Stars
Explanation: These separate radio images reveal three dusty debris disks surrounding three bright, young, nearby stars - evidence for solar systems in formation. From left to right are the stars Fomalhaut, Beta Pictoris, and Vega, their positions indicated by star symbols. The false color maps show the intensity of submillimeter radio emission from the surrounding dust. Next to each dust "disk", a vertical bar illustrates the present size of our own solar system. These observations are likely examples of what our solar system would have looked like to distant radio astronomers when it was only a few hundred million years old! Astronomers speculate that bright blobs of emission near Vega and Beta Pictoris may represent dust clouds around developing giant planets. The radio images were made using detectors cooled to near absolute zero and the James Clerk Maxwell Telescope at Mauna Kea Observatory in Hawaii.

APOD: April 22, 1998 - HR 4796A: A Recipe for Planets
Explanation: Two hundred and twenty light years from Earth, planets are forming. Recent observations of the binary star system HR 4796 have shown that one of the stars is surrounded by a dusty gaseous disk. This disk is of the right size, age, and density for dust pellets to accrete surrounding matter. A hole in the disk's center indicates that increasingly larger condensates are colliding and sticking together, coalescing into moons and planets. Pictured above is a false-color image of the system, with the bright star HR 4796A indicated by a cross. The disk measures about five times the size of our Solar System, and is seen nearly edge-on. HR 4796 is in the southern constellation Centaurus.

APOD: April 11, 1998 - NGC 604: Giant Stellar Nursery
Explanation: Scattered within this cavernous nebula, cataloged as NGC 604, are over 200 newly formed hot, massive, stars. At 1,500 light-years across, this expansive cloud of interstellar gas and dust is effectively a giant stellar nursery located some three million light-years distant in the spiral galaxy, M33. The newborn stars irradiate the gas with energetic ultraviolet light stripping electrons from atoms and producing a characteristic nebular glow. The details of the nebula's structure hold clues to the mysteries of star formation and galaxy evolution.

APOD: March 26, 1998 - Galaxies Away
Explanation: This striking pair of galaxies is far, far away ... about 350 million light-years from Earth. Cataloged as AM0500-620, the pair is located in the southern constellation Dorado. The background elliptical and foreground spiral galaxy are representative of two of the three major classes of galaxies which inhabit our Universe. Within the disks of spiral galaxies, like our own Milky Way, gas, dust, and young blue star clusters trace out grand spiral "arms". The dust lanes along the arms of this particular spiral stand out dramatically in this Hubble Space Telescope image as they obligingly sweep in front of the background elliptical. Like the central bulges of spiral galaxies, elliptical galaxies tend toward spherical shapes resulting from more random motions of their stars. But while spirals produce new stars, star formation in ellipticals which lack gas and dust seems to have stopped. How do galaxies evolve with cosmic time? Evidence is growing that graceful galaxy shapes can hide a violent history.

APOD: February 25, 1998 - The Solar Neighborhood
Explanation: You are here. The orange dot in the above false-color drawing represents the current location of the Sun among local gas clouds in the spiral Milky Way Galaxy. These gas clouds are so thin that we usually see right through them. Nearly spherical bubbles surround regions of recent star formation. The purple filaments near the Sun are gas shells resulting from star formation 4 million years ago in the Scorpius-Centaurus Association, located to the Sun's lower left. The Sun has been between spiral arms moving through relatively low density gas for the past 5 million years. In contrast, the Sun oscillates in the Milky Way plane every 66 million years, and circles the Galactic Center every 250 million years.

APOD: January 22, 1998 - Closer To Beta Pic
Explanation: What did our Solar System look like as the planets were forming? Since the 1980s, astronomers have been pointing toward Beta Pictoris, a young, sun-like star a mere 50 light-years distant, as a likely example. Beta Pic is surrounded by a disk of dust which we view nearly edge-on. The dust disk shines by reflected starlight and has been examined with ever increasing detail to search for signs of planetary formation. The trick is to follow the disk as close in to the star as possible, without being overwhelmed by the direct starlight. To make this Hubble Space Telescope image, a coronagraph was used to block the direct starlight and achieve the closest view yet. The false color picture shows the inner section of the dusty disk to within nearly 1.5 billion miles of the star itself, about the scale of the orbit of Uranus. The obvious warp is indirect evidence that a planet now orbits this young sun, slightly inclined to the disk. The planet's gravitational pull would produce the visible distortion.

APOD: December 24, 1997 - 30 Doradus Across the Spectrum
Explanation: 30 Doradus is lit up like a Christmas tree. Shining in light across the electromagnetic spectrum, 30 Doradus glows because of all the energetic processes that go on there. A distinctive region visible in a Milky Way satellite galaxy called the Large Magellanic Cloud (LMC), 30 Doradus is a hotbed of star formation, supernova explosions, and ionized plasma. The above image is a composite of three pictures taken in three different wavelength bands of light. Red represents X-ray emission created by gas as hot as 1 million degrees Kelvin. Green represents emission from ionized hydrogen gas, and blue represents ultraviolet radiation primarily emitted by hot stars. At the conclusion of this symphony of star formation and light in a few million years, astronomers expect that a new globular cluster will have formed.

APOD: October 22, 1997 - The Antennae Galaxies
Explanation: A ground-based telescopic view (left) of the collision between the galaxies NGC4038 and NGC4039 reveals long arcing insect-like "antennae" of luminous matter flung from the scene of the accident. Investigators using the Hubble Space Telescope to sift through the cosmic wreckage near the two galaxy cores have recently announced the discovery of over a thousand bright young clusters of stars - the result of a burst of star formation triggered by the collision. The green outline shows the area covered by the higher resolution Hubble image (right). At the distance of the Antennae galaxies (about 63 million light-years), a pixel in this image corresponds to about 15 light-years. Dust clouds around the two galactic nuclei give them a dimmed and reddened appearance while the massive, hot, young stars of the newly formed clusters are blue. How do colliding galaxies evolve with time? Determining the ages of star clusters formed in galaxy collisions can provide significant clues. The Antennae galaxies are seen in the southerly constellation Corvus.

APOD: July 30, 1997 - Eagle Castle
Explanation: What lights up this castle of star formation? The familiar Eagle Nebula glows much like a neon sign, but in many colors at once. The above photograph is a composite of three of these glowing gas colors. In particular the glowing red Sulfur gas of the nebula nicely outlines some of the denser star forming knots. Energetic light from young massive stars causes the gas to glow and effectively boils away part of the dust and gas from its birth pillar. Many of these stars will explode after several million years, returning most of their elements back to the nebula which formed them. This process is forming an open cluster of stars known as M16.

APOD: June 20, 1997 - NGC1850: Star Cluster in the LMC
Explanation: NGC1850 is a large cluster of stars located a mere 166,000 light-years from Earth in our neighboring galaxy the Large Magellanic Cloud (LMC). The colors in this beautiful Hubble Space Telescope composite image of the cluster reveal different populations of stars. Yellowish stars are the main cluster stars, sun-like main sequence hydrogen burners about 50 million years old. The white stars are massive, hotter, and younger, about 4 million years old. Radiating strongly in ultraviolet light, they represent a loose cluster themselves, perhaps within 200 light-years of the main cluster. Massive stars which formed in the older main cluster have long since disappeared, ending their lives in spectacular supernova explosions. Did expanding debris from these supernovae trigger the formation of the nearby younger cluster? Probably so. In any event, a few million years from now a similar fate awaits the massive stars of the younger cluster - burning brightly but briefly before they explode sending new clouds of stellar debris into space.

APOD: June 11, 1997 - Young Suns
Explanation: The star cataloged as NGC2264 IRS is normally hidden from the inquiring gaze of optical telescopes. It resides in the midst of the obscuring gas and dust of a nearby star forming region popularly known as the Cone Nebula. Imaged in penetrating infrared light by the Hubble Space Telescope's newly operational NICMOS instrument, this young and massive star was found to be surrounded by six "baby" sun-like stars - all within less than a tenth of a light-year of their "big brother". The diffraction spikes and rings surrounding big brother are image artifacts. Astronomers believe that the high speed winds generated by the massive star compressed nearby material causing the formation of the smaller stars in a text book example of triggered star formation. The newly created suns appear to lie along an otherwise invisible boundary where the high speed gas has collided with the wall of a denser molecular cloud. NGC2264 IRS also seems to be the source of the outflow which created the striking cone shape of the optical nebula.

APOD: December 11, 1996 - Starburst Ring in Galaxy NGC 1317
Explanation: Where do stars form? A typical place is an area of dense nebular gas common to arms in spiral galaxies. Sometimes, however, a burst of star formation can occur with unusual geometry. Nearby galaxy NGC 1317 shows such an unusual ring of star formation surrounding its barred nucleus. In the above image, older stars appear more red and are more evident in the leftmost photograph in visible light. The rightmost photograph taken by the Ultraviolet Imaging Telescope is in ultraviolet and highlights stars which are younger and bluer and shows the starbirth ring. This unusual ring may be evidence of a gravitational encounter with another galaxy, causing a density wave to ripple out from the galaxy's center.

APOD: October 14, 1996 - Bright Stars, Dim Galaxy
Explanation: These two clusters of bright, newly formed stars surrounded by a glowing nebula lie 10 million light years away in the dim, irregular galaxy cataloged as NGC 2366. The Hubble Space Telescope image shows that the youngest cluster, the bottom one at about 2 million years old, is still surrounded by the gas and dust cloud it condensed from, while powerful stellar winds from the stars in the older cluster at the top (4-5 million years old), have begun to clear away its central areas giving the entire nebula an apparent hook shape. Compared to the sun, the stars in these clusters are massive and short lived. The brightest one, near the tip of the hook, is a rare Luminous Blue Variable with 30 to 60 times the mass of the sun - similar to the erruptive Eta Carina variable in our own Milky Way. Stars this massive are extremely variable. A comparison with ground based images indicates that in three years this star's brightness increased by about 40 times making it currently the brightest star in this dim galaxy. Studies of such distant and diverse galaxies yield clues to the relationships of star formation and galactic evolution.

APOD: August 23, 1996 - NGC 3293: A Bright Young Open Cluster
Explanation: Hot Blue stars shine brightly in this beautiful, recently formed galactic or "open" star cluster. Open cluster NGC 3293 is located in the constellation Carina, lies at a distance of about 8000 light years, and has a particularly high abundance of these young bright stars. A study of NGC 3293 implies that the blue stars are only about 6 million years old, whereas the cluster's dimmer, redder stars appear to be about 20 million years old. If true, star formation in this open cluster took at least 15 million years. Even this amount of time is short, however, when compared with the billions of years stars like our Sun live, and the over-ten billion year lifetimes of many galaxies and our universe. NGC 3293 appears just in front dense dust lane emanating from the Carina Nebula.

APOD: October 1, 1995 - Central Galactic Star Bursts
Explanation: The pictured core of the galaxy NGC 253 shows an exceptionally high rate of star formation. In the center are some of the densest knots of stars ever found, surrounded by glowing gas and dust lanes. Galaxies where such high star formation rates are seen are called "starburst" galaxies. The unusual color is a combination of the light emitted from the young, hot, blue stars and their associated emission and reflection nebulae.