Astronomy Picture of the Day |
APOD: 2009 February 19 - Mauna Kea Milky Way Panorama
Explanation:
Aloha and welcome to a breathtaking skyscape.
The dreamlike panoramic view looks out from the 4,200 meter volcanic
summit of Mauna Kea, Hawai'i,
across a layer of clouds toward a
starry night sky
and the rising Milky Way.
Anchoring the scene on the far left is the dome of the
Canada-France-Hawaii Telescope (CFHT), with
north
star Polaris shining beyond the dome to the right.
Farther right, headed by bright
star Deneb,
the Northern Cross asterism
is embedded along the plane of the Milky Way as it peeks above the
horizon.
Both Northern Cross and
brilliant white
Vega
hang over a foreground grouping of cinder cones.
Near the center are the reddish nebulae, stars and dust clouds of
the central Milky Way.
Below, illumination from the city lights of Hilo creates
an eerie, greenish glow in the clouds.
Red supergiant
star
Antares shines above the Milky Way's central bulge
while bright
Alpha
Centauri lies still farther right, along
the dusty galactic plane.
Finally, at the far right is the large
Gemini North Observatory.
The compact group of stars known as the
Southern Cross is just
left of the telescope dome.
Need some help identifying the stars?
Just slide your cursor over the picture, or download this smaller,
labeled
panorama.
APOD: 2009 February 12 - Zodiacal Light Vs. Milky Way
Explanation:
Two fundamental planes of planet Earth's sky compete
for attention in this remarkable wide-angle vista,
recorded on January 23rd.
Arcing above the horizon and into the night at the left
is a beautiful band of
Zodiacal Light - sunlight scattered by
dust
in the solar system's ecliptic plane.
Its opponent on the right is composed of the
faint stars, dust clouds, and nebulae along
the plane of our
Milky Way Galaxy.
Both celestial bands stand above the domes and towers of the
Teide Observatory
on the island of Tenerife.
Also out to play in the pristine, dark skies over the Canary Islands,
are brilliant Venus (lower left),
the distant
Andromeda Galaxy (near center),
and the lovely
Pleiades star cluster (top center).
Of course, seasoned skygazers might even spot
M33, the
California Nebula,
IC1805, and the
double star cluster of Perseus.
(Need some help? Just slide your cursor over the picture.)
APOD: 2009 January 27 - The Milky Way Over Mauna Kea
Explanation:
Have you ever seen the band of our Milky Way Galaxy?
In a clear sky from a dark location at the right time, a faint band of light becomes visible across the sky.
Soon after your eyes become
dark adapted,
you might spot the band for the first time.
It may then become obvious.
Then spectacular.
One reason for a growing astonishment might be the realization that this
fuzzy swath
contains billions of stars and is the disk of our
very own
spiral galaxy.
Since we are inside this disk, the
band appears to encircle the Earth.
Visible in the above image, high above in the night sky, the
band of the Milky Way Galaxy arcs.
The bright spot just below the band is the planet Jupiter.
In the foreground lies the moonlit caldera of the volcano
Haleakala,
located on the island of
Maui in
Hawaii,
USA.
A close look near the horizon will reveal light clouds and the dark but enormous
Mauna Kea volcano on the
Big Island of Hawaii.
If you have never seen the Milky Way band or recognized the
planet Jupiter, this year may be your chance.
Because 2009 is the
International Year of Astronomy,
an opportunity to look through a
window that peers deep into the universe
may be coming to a location near you.
APOD: 2009 January 23 - Globular Cluster NGC 2419
Explanation:
Of three objects prominent in
this thoughtful telescopic image,
a view toward the stealthy constellation
Lynx,
two (the spiky ones) are nearby stars.
The third is the remote globular star cluster
NGC 2419,
at distance of nearly 300,000 light-years.
NGC 2419 is sometimes
called "the Intergalactic Wanderer",
an appropriate title considering that the distance to
the Milky Way's satellite galaxy, the
Large Magellanic Cloud, is only
about 160,000 light-years.
Roughly similar to other large globular star clusters like
Omega Centauri, NGC 2419
is itself intrinsically bright, but appears faint because
it is so far away.
NGC 2419 may really have an extragalactic origin as,
for example, the remains of a small galaxy
captured and disrupted by the Milky Way.
But its extreme distance makes it difficult to
study
and compare its properties with other
globular clusters that roam the halo of
our Milky Way galaxy.
APOD: 2009 January 7 - The Galactic Core in Infrared
Explanation:
What's happening at the center of our Milky Way Galaxy?
To help find out, the orbiting
Hubble and
Spitzer
space telescopes have combined their efforts to
survey the region in unprecedented detail in infrared light.
Infrared light is particularly useful for probing the
Milky Way's center
because visible light is more greatly obscured by
dust.
The above image encompasses over 2,000 images from the
Hubble Space Telescope's
NICMOS taken last year.
The image spans 300 by 115 light years with such high resolution that structures only 20 times the size of our own Solar System are discernable.
Clouds of glowing gas and
dark dust as well as three large star clusters are visible.
Magnetic fields
may be channeling
plasma
along the upper left near the
Arches Cluster,
while energetic
stellar winds are carving
pillars near the
Quintuplet Cluster on the lower left.
The massive Central Cluster of stars surrounding
Sagittarius A*
is visible on the lower right.
Why several central, bright, massive stars appear to be unassociated with
these star clusters is not yet understood.
APOD: 2008 December 19 - The Large Cloud of Magellan
Explanation:
The 16th century Portuguese navigator
Ferdinand
Magellan and his crew had plenty of time to study the
southern sky during the first circumnavigation of planet Earth.
As a result, two fuzzy cloud-like
objects easily visible to southern hemisphere skygazers are known as the
Clouds of Magellan,
now understood to be
satellite galaxies of our much larger, spiral Milky Way galaxy.
About 160,000 light-years distant in the constellation
Dorado,
the Large
Magellanic Cloud (LMC) is seen here in a remarkably detailed,
10
frame mosaic image.
Spanning about 30,000 light-years or so, it is
the most massive of the Milky Way's
satellite
galaxies and is the site of the
closest
supernova in modern times, SN 1987A.
The prominent reddish knot near the bottom is 30 Doradus, or the
Tarantula Nebula, a giant star-forming
region in the Large Magellanic Cloud.
To identify the location of the supernova and navigate your way
around the many star clusters and nebulae of the LMC, just consult this
well-labeled view.
APOD: 2008 December 11 - At the Center of the Milky Way
Explanation:
At the center of our Milky Way Galaxy lies a
supermassive black hole.
Once a controversial claim, this conclusion is now solidly based
on 16 years of observations
that map the orbits of 28 stars very near
the galactic center.
Using European Southern Observatory
telescopes and sophisticated
near infrared cameras, astronomers patiently measured the positions
of the stars over time, following one star, designated S2, through
a complete orbit as it came within about 1 light-day of the
center of the Milky Way.
Their results
convincingly show that S2 is moving under the influence of the
enormous gravity of a compact, unseen object -- a black hole
with 4 million times the mass
of
the Sun.
Their ability to track stars so close to the
galactic center
accurately measures the black hole's mass and also determines the
distance to the center to be 27,000 light-years.
This deep, near-infrared image shows the crowded inner 3
light-years of the central Milky Way.
Spectacular time-lapse animations of the stars orbiting
within light-days of the galactic center
can be found here.
APOD: 2008 November 29 - Chilean Skyscape
Explanation:
Night skies over Chilean mountain top observatories
can be dark and clear, with
glorious cosmic vistas.
In this recent example, the plane of our Milky Way galaxy stretches
parallel to the horizon,
the galactic center's star clusters,
dark dust clouds, and glowing nebulae hovering in the west.
Recorded after sunset, the wedge of light extending upward
through the scene is Zodiacal light,
sunlight scattered by dust
along the solar system's ecliptic plane.
A faint meteor was also caught in the view, but
approaching a conjunction, brilliant Venus and
bright Jupiter dominate the skyscape.
A close pairing through this weekend, by Monday,
December 1,
they will be joined by the young
crescent Moon.
Look west after sunset and the tight celestial triangle formed by
Moon, Venus, and Jupiter, the three brightest beacons in the night,
will be
a
spectacular sight,
even from bright-sky urban locations all over the world.
APOD: 2008 November 15 - Arp 273
Explanation:
The two prominent stars in the foreground of
this
colorful skyscape
are well within our own
Milky Way Galaxy.
Their spiky appearance
is due to diffraction in the astronomer's telescope.
But the two eye-catching galaxies in view lie far
beyond the Milky Way,
at a distance of about 200 million light-years.
Their distorted appearance is due to gravitational tides
as the pair engage
in
close encounters.
From our perspective, the bright cores of the galaxies are
separated by about 80,000 light-years.
Cataloged
as
Arp 273 (also as UGC 1810), the galaxies do look
peculiar,
but interacting galaxies are now understood to be
common in the universe.
In fact, the nearby large spiral Andromeda Galaxy is known to be
some 2 million light-years away and approaching the Milky Way.
Arp 273 may offer an analog of their
far future encounter.
Repeated galaxy encounters on a
cosmic timescale can ultimately
result in a merger into a single galaxy of stars.
APOD: 2008 November 10 - Our Galaxy's Central Molecular Zone
Explanation:
The central region of our Milky Way Galaxy is a mysterious and complex
place.
Pictured here in
radio
and infrared light, the galaxy's central square degree
is highlighted in fine detail.
The region is known as the
Central Molecular Zone.
While much of the extended emission is due to dense gas laced
with molecules, also seen are
emission nebulas
lit up by massive young stars, glowing
supernova remnants, and the
curving Galactic Center Radio Arc
in purple.
The identity and root cause for many other features remains unknown.
Besides a massive
black hole
named Sgr A*,
the Galactic Center houses the galaxy's most active star forming region.
This image is not just
interesting
scientifically.
It's esthetic
beauty won first prize this year in the
AUI/NRAO Image Contest.
APOD: 2008 September 29 - A True Image from False Kiva
Explanation:
Is there any place in the world you could see a sight like this?
Yes!
This digital mosaic
shows the night sky as seen from False Kiva in
Canyonlands National Park,
eastern Utah, USA.
Diving into the Earth far in the distance is part of the
central band of our
Milky Way Galaxy.
Much closer, the planet
Jupiter
is visible as the bright point just to band's left.
Closer still are the park's
picturesque
buttes and
mesas
lit by a crescent moon.
In the foreground is the cave housing a stone circle of unknown
origin named False Kiva.
The cave itself was briefly lit by flashlight during the exposure.
Astrophotographer
Wally Pacholka reports that getting to the cave
was no easy trek.
Also, mountain lions
were a concern while waiting alone in the dark to record the mosaic.
APOD: 2008 September 13 - M33: Triangulum Galaxy
Explanation:
The small, northern constellation
Triangulum
harbors this magnificent face-on spiral galaxy, M33.
Its popular names include the Pinwheel Galaxy or just
the Triangulum
Galaxy.
M33 is over 50,000 light-years in diameter, third largest in the
Local
Group of galaxies after the Andromeda Galaxy (M31), and our
own Milky Way.
About 3 million light-years from the Milky Way,
M33 is itself thought to be a satellite of the
Andromeda Galaxy and
astronomers
in these two galaxies would likely have spectacular views of
each other's grand spiral star systems.
As for the view from planet Earth, this
sharp, detailed
image nicely shows off M33's blue star clusters
and pinkish star forming regions that
trace the galaxy's loosely wound spiral arms.
In fact, the cavernous NGC 604 is the
brightest star forming region, seen here at about the 1 o'clock position
from the galaxy center.
Like M31, M33's population of well-measured variable stars
have helped make this nearby spiral a
cosmic
yardstick for
establishing
the distance scale of the Universe.
APOD: 2008 September 5 - Milky Way Road Trip
Explanation:
In search of planets and the summer
Milky Way,
astronomer Tunç Tezel took an evening
road trip.
Last Saturday, after driving the winding road up
Uludag,
a mountain near Bursa, Turkey, he was rewarded by this beautiful
skyview to the south.
Near the center, bright planet Jupiter outshines
the city lights below and the stars of the constellation
Sagittarius.
Above the mountain peaks, an arcing
cloud bank seems to lead to the Milky Way's own
cloudy apparition plunging into the distant horizon.
In Turkish, Uludag
means Great Mountain.
Uludag was known in
ancient times
as the Mysian Olympus.
APOD: 2008 August 6 - NGC 1818: A Young Globular Cluster
Explanation:
Globular clusters once ruled the
Milky Way.
Back in the
old days, back when our Galaxy first
formed, perhaps thousands of globular clusters roamed
our Galaxy.
Today, there are
perhaps 200 left.
Many
globular clusters were destroyed
over the eons by repeated fateful encounters
with each other or the
Galactic center.
Surviving relics are older than any Earth fossil,
older than any
other structures in our Galaxy, and
limit the
universe itself in raw age.
There are few, if any, young
globular clusters in our
Milky Way Galaxy because
conditions are not ripe for more to form.
Things are different next door, however, in the neighboring
LMC galaxy.
Pictured above is a "young" globular cluster residing there:
NGC 1818.
Observations show it formed
only about 40 million years ago -
just yesterday compared to the 12 billion year ages of
globular clusters in our own
Milky Way
APOD: 2008 July 29 - The Milky Way Over Ontario
Explanation:
Sometimes, after your eyes adapt to the dark, a spectacular sky appears.
Such was the case earlier this month over
Ontario,
Canada,
when part of a spectacular sky also became visible in a reflection off a lake.
To start, the brightest objects visible are bright stars and the
planet Jupiter, seen as the brightest spot on the upper left.
A distant town appears as a diffuse glow over the horizon.
More faint still, the disk of the
Milky Way Galaxy
becomes apparent as a dramatic diffuse
band
across the sky that seems to crash into the horizon far in the distance.
In the foreground, a picturesque landscape includes
trees, a lake, and a
stone wall.
Finally, on this serene night in July when the lake water was unusually calm,
reflections appear.
Visible in the lake are not only reflections of several bright stars, but part of the
Milky Way band itself.
Careful inspection of the image will reveal, however, that bright stars leave small trails in the lake reflections that do not appear in the
sky above.
The reason for this is because the above image is actually a
digital composite of time-consecutive
exposures from the same camera.
In the first set of exposures, sky images were co-added with slight
rotations to keep the stars in one place.
APOD: 2008 July 25 - Spitzer's M101
Explanation:
Big, beautiful spiral galaxy M101 is one of the last
entries in Charles Messier's
famous catalog, but definitely not
one of the least.
About 170,000 light-years across,
this galaxy is enormous, almost
twice the size of our own Milky Way Galaxy.
M101 was also one of the original
spiral
nebulae
observed by Lord Rosse's large 19th century telescope, the
Leviathan
of Parsontown.
Recorded at
infrared wavelengths
by the Spitzer Space telescope, this
21st century view
shows starlight in blue hues while the galaxy's
dust clouds are in red.
Examining the dust features in the outer rim of the
galaxy,
astronomers
have found that organic molecules present throughout
the rest of M101 are lacking.
The organic molecules tracked by Spitzer's instruments are
called polycyclic aromatic hydrocarbons
(PAHs).
Of course, PAHs are common components of dust in the
Milky Way
and on planet Earth are found in soot.
PAHs are likely destroyed near the outer edges of M101 by energetic
radiation in intense star forming regions.
Also known as the
Pinwheel Galaxy,
M101 lies within the boundaries of the northern constellation
Ursa Major, about 25 million light-years away.
APOD: 2008 July 18 - Jupiter over Ephesus
Explanation:
A brilliant Jupiter shares the sky with the Full Moon tonight.
Since
Jupiter is near
opposition,
literally opposite
the Sun in planet Earth's sky, Jupiter will rise near sunset
just
like the Full Moon.
Of course, opposition is also the point of closest approach, with
Jupiter shining at its brightest and offering the best
views for skygazers.
Recorded late last month, this moving skyscape features
Jupiter
above the southeastern horizon and the marbled streets of the
ancient port city of
Ephesus,
located in modern day Turkey.
At the left is
a temple
dedicated
to the Roman emperor
Hadrian.
The beautiful night sky also includes the arc of
the northern summer Milky Way.
Lights on the horizon are from the nearby town of Selçuk.
Clicking on the image will download the scene as a panorama.
APOD: 2008 July 13 - A Dark Sky Over Death Valley
Explanation:
This eerie glow over Death Valley is in danger.
Scrolling right will show a spectacular view from one of the
darkest places left in the continental
USA:
Death Valley,
California.
The above 360-degree full-sky panorama is a composite of 30 images taken two years ago in
Racetrack Playa.
The image has been digitally processed and increasingly stretched at high altitudes to make it rectangular.
In the foreground on the image right is an
unusually placed rock
that was pushed by high winds onto
Racetrack Playa
after a slick rain.
In the background is a
majestic night sky,
featuring thousands of stars and many constellations.
The arch across the middle is the central
band of our
Milky Way Galaxy.
Light pollution
is threatening dark skies like this all
across the US and the world, and therefore the
International Dark-Sky Association and the
US National Parks Service are
suggesting methods that can
protect
them.
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 July 8 - In the Heart of the Virgo Cluster
Explanation:
The Virgo Cluster of Galaxies
is the closest cluster of galaxies to our
Milky Way Galaxy.
The Virgo Cluster
is so close that it spans more than 5 degrees on the sky - about 10 times the angle made by a
full Moon.
With its heart lying about 70 million light years distant,
the Virgo Cluster
is the nearest
cluster of galaxies, contains over 2,000 galaxies,
and has a noticeable gravitational pull on the galaxies of the
Local Group of Galaxies surrounding our
Milky Way Galaxy.
The cluster contains not only galaxies filled with stars but also
gas so hot it glows in
X-rays.
Motions of galaxies in and around clusters indicate that they contain more
dark matter than any visible matter we can see.
Pictured above, the heart of the
Virgo Cluster
includes bright
Messier galaxies such as
Markarian's Eyes on the upper left,
M86 just to the upper right of center,
M84 on the far right,
as well as spiral galaxy NGC 4388 at the bottom right.
APOD: 2008 July 7 - The Southern Cross in a Southern Sky
Explanation:
This breathtaking patch of sky would be above you were you
to stand at the
South Pole of the Earth.
On the upper left of this image are the
four stars that mark the
boundaries of the famous
Southern Cross.
At the top of this constellation, also known as
The Crux,
is the orange star
Gamma Crucis.
The band of stars, dust, and gas
crossing the middle of the photograph is part our
Milky Way Galaxy.
Just below the Southern Cross on the far left is the dark
Coal Sack Nebula, and the bright nebula on the far right is the
Carina Nebula.
The Southern Cross is such a famous constellation that it is
depicted on the national flag of Australia.
APOD: 2008 June 28 - Fireball at Ayers Rock
Explanation:
A weekend trip for astrophotography in central
Australia can
result in gorgeous skyscapes.
In this example recorded in March of 2006,
the center of our
Milky Way Galaxy rises over planet Earth's
horizon and the large sandstone formation called Uluru,
also known as Ayers Rock.
After setting up two cameras to automatically image this
celestial scene in a series of exposures,
one through a wide-angle and the other through a telephoto lens,
photographer Joseph Brimacombe briefly turned his back
to set up other equipment.
To his surprise, the ground around him suddenly lit up with
the brilliant flash of a
fireball meteor.
To his delight, both cameras captured the
bright meteor
streak.
Highlighted in the telephoto view (inset), the fireball trail
shines through cloud banks, just left of
Ayers Rock.
APOD: 2008 June 6 - Two-Armed Spiral Milky Way
Explanation:
Gazing out from within
the Milky Way, our own galaxy's true structure is difficult to discern.
But an
ambitious survey effort with the
Spitzer Space Telescope now
offers convincing evidence
that we live in a large galaxy distinguished by two main
spiral arms
(the Scutum-Centaurus and Perseus arms)
emerging from the ends of a large central bar.
In fact, from a vantage point that viewed our galaxy
face-on,
astronomers in distant galaxies
would likely see
the Milky Way
as a two-armed barred spiral
similar to this
artist's illustration.
Previous investigations have identified
a smaller central barred structure and four spiral arms.
Astronomers still
place the Sun about a third of the way in from
the Milky Way's outer edge, in a minor arm called
the Orion Spur.
To locate the Sun and identify the Milky Way's newly mapped features,
just place your cursor over the image.
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 May 3 - Alborz Mountain Milky Way
Explanation:
Snow-capped stratovolcano
Mt. Damavand climbs to 5,670 meters
(18,598 feet) near the left edge in this panoramic view of
the world at
night.
In the sky to the left of Damavand's peak are the stars of the
Big Dipper in Ursa Major.
Pan to the right and your gaze will sweep across the arch of
our Milky Way Galaxy above the
Alborz Mountain Range
bordering the Caspian Sea.
Near the center of the panorama, recorded in the predawn
hours of April 4th, bright stars
Deneb and
Altair
lie close to the curve of the Milky Way, above the glow of
the Haraz valley.
Farther right, brilliant Jupiter dominates the sky
near the stars, nebulae, and dark dust clouds toward the
bulging galactic center.
Finally, the horizon glow at the right edge,
below bright yellowish giant star
Antares,
is from the city of Damavand, named for the legendary
mountain peak.
APOD: 2008 March 29 - Spiral Galaxy NGC 2841
Explanation:
Some 50 million light-years distant, spiral galaxy NGC 2841
can be found in the northern constellation of
Ursa Major.
This sharp view of the
gorgeous island universe
shows off a striking yellow nucleus and galactic disk with tightly
wound
spiral arms.
NGC 2841 has a diameter of over 150,000 light-years, even larger than
our own
Milky Way Galaxy.
The galaxy's dust lanes and turbulent star-forming regions are found
along the spiral arms, but
X-ray images
suggest that resulting winds and stellar explosions create
plumes of hot gas extending into a halo around NGC 2841.
Of course, the prominent stars with a
spiky appearance in
the picture are close foreground objects within the Milky Way
and not associated with
NGC 2841.
APOD: 2008 March 9 - CMBR Dipole: Speeding Through the Universe
Explanation:
Our Earth is not at rest.
The Earth moves around the Sun.
The Sun orbits the center of the
Milky Way Galaxy.
The Milky Way Galaxy orbits in the
Local Group of Galaxies.
The Local Group falls toward the
Virgo Cluster of Galaxies.
But these speeds are less than the speed that
all of these objects together move relative to the
cosmic microwave background radiation (CMBR).
In the
above all-sky map from the
COBE satellite,
radiation in the Earth's direction of motion appears
blueshifted and hence hotter, while
radiation on the opposite side of the sky is
redshifted and colder.
The map indicates that the
Local Group moves at about 600 kilometers per second relative to this
primordial radiation.
This high speed was initially unexpected and its magnitude is still unexplained.
Why are we moving so fast?
What is out there?
APOD: 2008 February 16 - Large Binocular Telescope
Explanation:
With moonlight on the horizon, a starry sky
and the northern Milky Way
provide the background for
this
dramatic view of the
World at Night.
The imposing structure in the foreground houses the
Large Binocular Telescope
(LBT), on Mount Graham, Arizona.
Inside,
the two 8.4 meter diameter mirrors of the LBT really are
side-by-side on a common mount, an
arrangement
mimicking the design of more modest optical equipment usually
carried around the neck.
While not exactly portable,
the benefits of the large scale binocular configuration adopted
include an increase in sensitivity over a single mirror telescope
and high resolution imaging for faint objects over a relatively
wide field of view.
An international collaboration operates the
LBT Observatory.
APOD: 2008 January 24 - Andromeda Island Universe
Explanation:
The most distant object easily visible to the unaided
eye is
M31,
the great
Andromeda Galaxy
some two and a half million light-years away.
But without a telescope, even this
immense spiral galaxy - spanning over
200,000 light years - appears as a faint, nebulous cloud in the
constellation
Andromeda.
In contrast, a bright yellow nucleus, dark winding dust lanes,
gorgeous blue spiral arms and star clusters are recorded in this
stunning telescopic
digital mosaic.
While even casual
skygazers
are now inspired by the knowledge that there are
many distant galaxies like M31, astronomers
seriously debated
this fundamental concept less than 90 years ago.
Were these "spiral nebulae" simply outlying components of our own
Milky Way Galaxy or were they instead "island universes" -- distant
systems of stars comparable to the Milky Way itself?
This question was central to the famous
Shapley-Curtis
debate
of 1920, which was later resolved by
observations of M31
in favor of Andromeda,
island
universe.
APOD: 2008 January 11 - Polaris Dust Nebula
Explanation:
Centered on North Star
Polaris,
this 4 degree wide
field of
view covers part of a complex of
relatively
unfamiliar, diffuse dust clouds
soaring high
above the plane of our Milky Way Galaxy.
The combined light of the
Milky Way stars are reflected by the dusty,
galactic cirrus,
the reflected starlight having the same blue tint
characteristic of better known
reflection nebulae.
But this deep color image also records a faint reddish
luminescence from the dust grains as they
convert invisible stellar ultraviolet radiation to
visible red light.
Dubbed
extended red emission,
the dim
cosmic glow
is thought to be caused by complex organic molecules
known as PAHs
(polycyclic aromatic hydrocarbons), common
constituents of
interstellar dust.
On planet Earth, PAHs are widely encountered as the sooty
products of combustion.
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: 2008 January 4 - The Milky Way at 5000 Meters
Explanation:
Climb up to 5000 meters (16,500 feet) above sea level, near
Cerro Chajnantor
in the northern
Chilean Andes,
and your night sky could encompass this cosmic vista.
Recorded from that
high and dry
locale, the spectacular fish-eye image features the myriad stars
and sprawling dust clouds of our
Milky Way Galaxy.
The direction toward the
center of the Galaxy is near the zenith
and center of the picture, but the
Galactic Center itself is hidden
from view, located far behind the obscuring dust.
Brilliant Jupiter rules this scene just above the
Milky Way's
central bulge with the noticeably fainter, yellowish,
giant star
Antares
to its right.
Small and faint, near the right edge of the picture is
one of the Milky Way's many
satellite
galaxies, the
Small Magellanic Cloud.
APOD: 2007 December 19 - Stars and Dust through Baade s Window
Explanation:
Billions of stars light up the direction toward the
center of our Galaxy.
The vast majority of these stars are themselves
billions of years old, rivaling their home
Milky Way Galaxy
in age.
Together with interstellar dust,
these
old stars combine to create this
yellowish starscape.
Although the
opaque dust obscures the
true Galactic center in
visible light, there is a low density hole in the
dust on the right of the image.
The region, named
Baade's
Window for the German
astronomer who studied it, is
used to inspect
distant stars and to determine the
internal geometry of the Milky Way.
Baade's Window
lies toward the constellation of the Archer (Sagittarius).
APOD: 2007 November 4 - The Closest Galaxy: Canis Major Dwarf
Explanation:
What is the closest galaxy to the Milky Way?
The new answer to this old question is the
Canis Major dwarf galaxy.
For many years astronomers thought the
Large Magellan Cloud
(LMC) was closest, but its title was supplanted in 1994 by the
Sagittarius dwarf galaxy.
Recent measurements indicate that the Canis Major dwarf is only 42,000 light years from the
Galactic center,
about three quarters of the distance to the
Sagittarius dwarf
and a quarter of the distance to the LMC.
The discovery was made in data from the
2MASS-sky survey, where infrared light allows a better view through our optically opaque
Galactic plane.
The labeled illustration above shows the location
of the newly discovered Canis Major dwarf and its associated
tidal stream of material in relation to our
Milky Way Galaxy.
The Canis Major dwarf
and other satellite galaxies are slowly being
gravitationally ripped apart as they travel around and through our Galaxy.
APOD: 2007 October 20 - The Milky Road
Explanation:
Inspired during a visit to Fort Davis, Texas, home of
McDonald Observatory
and dark night skies,
photographer Larry Landolfi created this tantalizing
fantasy view.
The composited
image suggests the Milky Way is a heavenly
extension of a deserted country road.
Of course, the
name for our galaxy, the
Milky Way
(in Latin, Via Lactea), does refer to its appearance
as a milky band or path in the sky.
In fact, the word galaxy itself derives from the Greek for
milk.
Visible on
moonless nights
from dark sky areas,
though not so colorful as in this image, the glowing
celestial
band is due to the collective light of myriad stars along the plane
of our galaxy, too faint to be distinguished individually.
The diffuse starlight is cut by dark swaths of
obscuring galactic dust clouds.
At the beginning of the 17th century, Galileo turned his
telescope on the Milky Way and announced it to be composed of
innumerable
stars.
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 October 1- The Small Cloud of Magellan
Explanation:
Portuguese navigator
Ferdinand Magellan
and his crew had plenty
of time to study the southern sky during the
first circumnavigation of planet Earth.
As a result, two celestial wonders
easily visible for southern hemisphere skygazers
are known as the Clouds of Magellan.
These cosmic clouds are now understood to be dwarf
irregular galaxies,
satellites of our larger spiral
Milky Way Galaxy.
The Small
Magellanic Cloud
pictured above actually spans 15,000 light-years or so
and contains several hundred million stars.
About 210,000 light-years distant in
the constellation
Tucana,
it is the fourth closest of the Milky Way's
known satellite galaxies, after the
Canis Major
and
Sagittarius
Dwarf galaxies and the
Large
Magellanic Cloud.
This gorgeous view also includes two foreground globular
star clusters NGC 362 (bottom right) and 47 Tucanae.
Spectacular 47 Tucanae
is a mere 13,000 light-years away and seen here to the left of the
Small Magellanic Cloud.
APOD: 2007 September 30 - A Milky Way Band
Explanation:
Most bright stars in our
Milky Way Galaxy reside in a disk.
Since our Sun also resides in this disk, these stars
appear to us as a
diffuse band that circles the sky.
The above panorama of a
northern band of the
Milky Way's disk covers 90 degrees and is a
digitally created mosaic of several independent exposures.
Scrolling right will display the rest of this spectacular picture.
Visible are many
bright stars,
dark dust lanes,
red emission nebulae,
blue reflection nebulae, and
clusters of stars.
In addition to all this matter that we can see,
astronomers suspect there exists even more
dark matter that we cannot see.
APOD: 2007 September 11 - A Scorpius Sky Spectacular
Explanation:
If Scorpius looked this good to the unaided eye, humans might remember it better.
Scorpius
more typically appears as a few bright stars in a well known but rarely pointed out
zodiacal
constellation.
To get a spectacular image like
this, though, one needs a good
camera, color
filters,
and a digital image processor.
To bring out detail, the
above image not only involved long duration exposures taken in several colors,
but one exposure in a
very specific red color emitted by
hydrogen
that brings out great detail.
The resulting image shows many breathtaking features.
Vertically across the image left is part of the
plane of our
Milky Way Galaxy.
Visible there are vast clouds of bright stars and long filaments of dark
dust.
Jutting out diagonally from the
Milky Way in the image center are
dark dust bands known as the
Dark River.
This river connects to several bright stars on the right that are part of
Scorpius' head and claws,
and include the bright star
Antares.
Above and right of Antares is an even brighter planet Jupiter.
Numerous red
emission nebulas and blue
reflection nebulas
are visible throughout the image.
Scorpius
appears prominently in southern skies after sunset during the middle of the year.
APOD: 2007 July 21 - Infrared Andromeda
Explanation:
This wide, detailed
Spitzer Space Telescope view
features infrared light from dust (red) and old stars (blue)
in Andromeda, a massive spiral galaxy
a mere 2.5 million light-years away.
In fact, with over twice the diameter of
our own Milky Way,
Andromeda is
the largest nearby galaxy.
Andromeda's population of bright young stars define its sweeping
spiral arms in
visible light images, but here
the infrared view clearly follows the lumpy dust lanes heated by
the young stars as they wind even closer to the
galaxy's core.
Constructed to explore Andromeda's
infrared brightness
and
stellar populations, the full mosaic image is composed of
about 3,000 individual frames.
Two smaller companion galaxies,
NGC 205 (below) and
M32 (above)
are also included in the combined fields.
The data confirm that Andromeda (aka M31) houses around 1
trillion
stars, compared
to
4 hundred
billion
for the Milky Way.
APOD: 2007 July 12 - NGC 6384: Beyond the Stars
Explanation:
The universe is filled
with
galaxies.
But to see them astronomers must
look out beyond the stars of
our galaxy,
the Milky Way.
For example,
consider this
colorful telescopic view of
spiral galaxy NGC 6384, about 80 million light-years
away in the direction of the constellation Ophiuchus.
At that distance, NGC 6384 spans an estimated 150,000 light-years.
The sharp image shows details in the distant galaxy's blue spiral
arms and yellowish core.
Still, the individual stars seen in the picture
are all in the close foreground, well
within our own
galaxy.
The brighter Milky Way stars show noticeable crosses, or
diffraction spikes,
caused by the telescope itself.
This particular field of view is about 1/4 degree wide and
is relatively rich in foreground stars because it
looks out
near the crowded center of the Milky Way.
APOD: 2007 July 11 - Constellations and Cloudy Skies
Explanation:
Recorded earlier in July, the clouds of
planet Earth
reflect moonlight and a faint, reddish glow in
this serene sea and skyscape.
Beyond them lie the cosmic dust and star clouds of
the Milky Way.
The near-midnight view
looks south from a beach in northern France and finds
the constellation Sagittarius, the Archer,
peaking above the horizon.
Bright planet
Jupiter rules on the right, wandering
among the stars of the constellation
Scorpius.
Of course, the Galactic Center itself
is hidden behind the
Milky Way clouds in Sagittarius.
To find them, just put your cursor over the picture and
follow the arrow.
APOD: 2007 May 25 - Jupiter, Vesta, and the Milky Way
Explanation:
In this gorgeous skyscape, gas giant Jupiter
along with the stars and cosmic dust clouds
of the Milky Way
hang over the southern horizon in the
early morning hours as seen from Stagecoach, Colorado, USA.
Recorded on Thursday, Jupiter is the brightest object near picture
center.
Along with the stunning Milky Way, Jupiter is hard to miss,
but a
careful
inspection of the view also reveals
main belt
asteroid Vesta.
Of all the asteroids
Vesta is the brightest and
is now just bright enough to be visible to the naked eye
from locations with very dark, clear skies.
Vesta (as well as Jupiter) appears relatively
bright now because it is near opposition, literally opposite the Sun
in planet Earth's sky and closest to Earth in its orbit.
For Vesta, this opposition
offers the best viewing in many years.
The year 2007 also
coincides
with the 200th anniversary of
the asteroid's
discovery.
Starting late next month, NASA plans to launch the
Dawn mission intended
to explore Vesta (and Ceres) and the main asteroid belt.
APOD: 2007 May 17 - The Milky Way Near the Southern Cross
Explanation:
The glow of the southern Milky Way
and the well-known
Southern Cross
are featured in this colorful skyscape
recorded in April over La Frontera, Chile.
The Southern Cross
(Crux)
itself is at the right of the
20 degree wide field of view, topped by bright,
yellowish star
Gamma Crucis.
A line from Gamma Crucis through the blue
star at the bottom of the cross, Alpha Crucis,
points toward the south celestial pole.
Against faint Milky Way starlight, the dark expanse of the
Coal
Sack Nebula lies just left of the cross,
while farther left along the Milky Way are the bright stars
Hadar
and
Rigil
Kentaurus, also known as
Beta and Alpha
Centauri.
Blazing in the lower left, Alpha Cen is the closest star
to the Sun, a mere 4.3 light-years distant.
In fact, yellowish Alpha Cen is
actually a triple star
system that includes a sun-like star.
Seen
from Alpha Cen, our own Sun would be a bright yellowish
star in the otherwise recognizable constellation Cassiopeia.
APOD: 2007 May 15 - Bright Spiral Galaxy M81 in Ultraviolet from Galex
Explanation:
Where are the hot stars in M81, one of the closest major spiral galaxies?
To help find out, astronomers took a deep image in
ultraviolet light
of the sprawling spiral with the Earth-orbiting
Galex telescope.
Hot stars emit more ultraviolet than cool stars, and are frequently associated with young
open clusters of stars and energetic
star forming regions.
Magnificent
spiral galaxy M81, slightly smaller in size to our own
Milky Way Galaxy,
shows off its young stars in its winding spiral arms in the
above image.
Less than 100 million years old, the young stars are blue in the
above false-color Galex image and seen to be well separated from the
older yellowish stars of the galactic core.
Visible above
M81 is a satellite galaxy dubbed
Holmberg IX.
Studying the unexpectedly bright ultraviolet glow of this small
irregular galaxy
may help astronomers understand how the
many satellites
of our own Milky Way Galaxy developed.
M81,
visible through a small telescope, spans about 70,000
light years
and lies about 12 million light years away toward the
constellation of the Great Bear
(Ursa Major).
APOD: 2007 April 27 - M81 in Ursa Major
Explanation:
One of the brightest galaxies in planet Earth's sky and similar in size
to the Milky Way,
big, beautiful spiral M81
lies 11.8 million light-years away
in the northern constellation Ursa Major.
This remarkably deep image
of the region reveals details in the bright
yellow core, but at the
same time follows fainter features along the galaxy's gorgeous blue
spiral arms and
sweeping dust lanes.
Above M81 lies a dwarf companion galaxy,
Holmberg IX,
sporting a large,
pinkish star-forming
region near the top.
While M81
and Holmberg IX are seen through a foreground of stars in our
own Milky Way galaxy, they
are also seen here through a much fainter complex of dust clouds.
The relatively unexplored clouds
are likely only some hundreds of light-years distant and lie high
above our galaxy's plane.
Scattered through the image, especially at the the right, the dust
clouds reflect the combined light of the
Milky Way's stars and have been dubbed
integrated
flux nebulae.
APOD: 2007 April 19 - NGC 5139: Omega Centauri
Explanation:
Centaurus
is one of the most striking constellations in
the southern sky.
The Milky Way flows through this
celestial expanse
whose wonders also include the closest star system to the Sun,
Alpha Centauri,
and the largest globular star cluster in our galaxy,
Omega Centauri
(aka NGC 5139).
This sharp
telescopic view of Omega Centauri shows off the central
regions of the cluster of about 10 million stars.
Omega Cen itself
is about 15,000 light-years away and 150 light-years in diameter - the
largest of 150 or so
known
globular star clusters that roam the halo of
our galaxy.
Though most star clusters consist of stars with the same age and
composition, the enigmatic Omega Cen
exhibits the
presence of different stellar populations with a spread of ages
and chemical abundances.
In fact, Omega Cen may be the remnant core
of a small galaxy
merging
with the Milky Way.
APOD: 2007 March 30 - Three Galaxies and a Comet
Explanation:
Diffuse starlight and dark nebulae
along the southern
Milky Way
arc over the horizon and sprawl diagonally through this
gorgeous nightscape.
The breath-taking mosaic spans a wide
100 degrees, with the rugged
terrain
of the Patagonia, Argentina region in the foreground.
Along with the insider's view of our own galaxy, the image
features our outside perspective on two irregular satellite galaxies -
the Large and
Small Magellanic Clouds.
Recorded on January 28, the scene also captures the
broad tail
and bright coma of Comet McNaught, The
Great Comet of 2007.
APOD: 2007 February 12 - Comet McNaught Over New Zealand
Explanation:
Comet McNaught is perhaps the most photogenic comet of our time.
After making
quite a show in the northern hemisphere in mid January,
the comet moved south and developed a
long and unusual dust tail that
dazzled southern hemisphere observers starting in late January.
Comet McNaught
was imaged two weeks ago between Mount Remarkable and Cecil Peak in this
spectacular image
taken from
Queenstown,
South Island,
New Zealand.
The bright comet dominates the right part of the
above image, while the
central band of our
Milky Way Galaxy
dominates the left.
Careful inspection of the image will reveal a
meteor streak just to the left of the comet.
Comet McNaught continues to move out from the Sun and dim, but should remain
visible in southern skies with binoculars through the end of this month.
APOD: 2007 February 10 - Stars of the Galactic Center
Explanation:
The center
of our Milky Way Galaxy
is hidden
from the prying eyes of optical telescopes by clouds of
obscuring dust and gas.
But in this stunning vista,
the Spitzer Space Telescope's
infrared cameras, penetrate
much of the dust revealing
the stars of the crowded galactic center region.
A mosaic of many smaller snapshots, the detailed,
false-color image shows
older, cool stars in bluish hues.
Reddish glowing dust clouds are associated with
young, hot stars in stellar nurseries.
The galactic center
lies some 26,000 light-years away, toward the constellation
Sagittarius.
At that distance, this picture spans about 900 light-years.
APOD: 2007 January 23 - The Milky Way Over Paranal
Explanation:
It's not the sky that's falling. More accurately,
the Earth is rising.
The Earth's rotation gives a continually changing view to all Earth observers,
including those measuring the universe at the
Paranal Observatory.
The observatory's four, massive 8.2 meter telescope units
are situated on top of the 2,600 meter high mountain,
Cerro Paranal,
in the dry Atacama Desert in northern Chile.
The individual unit
telescopes can be used separately or in combination.
Their names, Antu, Kueyen, Melipal, and
Yepun, are taken from
the Mapuche language.
Fittingly they translate to Sun, Moon, Evening Star, and
Southern Cross.
Together they are fittingly known as the
European Southern Observatory's
Very Large Telescope.
A higher time resolution version of the above movie is available here.
APOD: 2006 October 8 - CMBR Dipole: Speeding Through the Universe
Explanation:
Our Earth is not at rest.
The Earth moves around the Sun.
The Sun orbits the center of the
Milky Way Galaxy.
The Milky Way Galaxy orbits in the
Local Group of Galaxies.
The Local Group falls toward the
Virgo Cluster of Galaxies.
But these speeds are less than the speed that
all of these objects together move relative to the
cosmic microwave background radiation (CMBR).
In the
above all-sky map from the COBE satellite, radiation in the
Earth's direction of motion appears
blueshifted and hence hotter,
while radiation on the opposite side of the sky is
redshifted and colder.
The map indicates that the
Local Group moves at about 600 kilometers per second relative to this
primordial radiation.
This high speed was initially unexpected and its magnitude is still unexplained.
Why are we moving so fast?
What is out there?
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 September 24 - NGC 1499: The California Nebula
Explanation:
What's California doing in space?
Drifting through the Orion Arm of the spiral Milky Way Galaxy,
this cosmic cloud
by chance echoes the outline of
California
on the west coast of the
United States.
Our own Sun also lies within the Milky Way's
Orion
Arm, only about 1,500 light-years from the
California Nebula.
Also known as NGC 1499, the classic emission nebula is around 100
light-years long.
It glows with the red light characteristic of hydrogen atoms
recombining with
long
lost electrons, stripped away (ionized)
by energetic starlight.
In this case, the star most likely providing the energetic
starlight is the bright, hot, bluish Xi Persei,
just right of the nebula and above picture center.
Fittingly, this
composite picture was made with images from a telescope
in California - the 48-inch (1.2-meter)
Samuel
Oschin Telescope - taken as a part of the second National Geographic
Palomar Observatory
Sky Survey.
APOD: 2006 September 14 - M33: Spiral Galaxy in Triangulum
Explanation:
The small, northern constellation
Triangulum
harbors this magnificent face-on spiral galaxy, M33.
Its popular names include the Pinwheel Galaxy or just
the Triangulum
Galaxy.
M33 is over 50,000 light-years in diameter, third largest in the
Local
Group of galaxies after the Andromeda Galaxy (M31), and our
own Milky Way.
About 3 million light-years from the Milky Way,
M33 is itself thought to be a satellite of the
Andromeda Galaxy and
astronomers
in these two galaxies would likely have spectacular views of
each other's grand spiral star systems.
As for the view from planet Earth, this
detailed,
wide field image nicely shows off M33's blue
star clusters
and pinkish star forming regions which
trace the galaxy's loosely wound spiral arms.
In fact, the cavernous NGC 604 is the
brightest star forming region, seen here at about the 1 o'clock position
from the galaxy center.
Like M31, M33's population of well-measured variable stars
have helped make this nearby spiral a
cosmic
yardstick for
establishing
the distance scale of the Universe.
APOD: 2006 August 9 - Magellanic Morning
Explanation:
This
early morning skyscape
recorded near Winton, Queensland, Australia,
looks toward the southeast.
Low clouds are seen in silhouette against the first hints
of sunlight, while two famous cosmic clouds, the
Clouds
of Magellan, also hover in the brightening sky.
The Small
Magellanic Cloud (SMC, upper right), and the
Large Magellanic Cloud (LMC) are prominent
wonders of the southern sky, named for the 16th century
Portuguese explorer
Ferdinand
Magellan.
They are small, irregular galaxies in their own right,
satellites of
our much larger, spiral Milky Way galaxy.
The SMC is about 210,000 light-years and the LMC about
180,000 light-years away.
At lower left,
bright
star Canopus (Alpha Carinae), denizen of the Milky Way,
is a mere 310 light-years distant.
APOD: 2006 August 1 - The Milky Way over Utah
Explanation:
If sometimes it appears that the entire
Milky Way Galaxy
is raining down on your head, do not despair.
It happens twice a day.
As the Sun rises in the East,
wonders of the night sky
become less bright than the
sunlight scattered by our own
Earth's atmosphere, and so fade from view.
They will only rotate
back into view when the Earth again eclipses our bright Sun at dusk.
This battle between heaven and Earth was
captured dramatically over a rock formation at
Capitol Reef National Park
Utah,
USA in 2003 May.
Dark dust,
millions of stars, and bright
glowing red gas highlight the
plane of our
Milky Way Galaxy,
which lies on average thousands of
light years behind
Earth's mountains.
APOD: 2006 June 23 - East of Antares
Explanation:
East of Antares, dark markings seem
to sprawl through the crowded star fields
toward the center of our Milky Way Galaxy.
Cataloged in the early 20th
century by astronomer
E. E. Barnard, the obscuring
interstellar dust clouds
include
B72,
B77, B78, and B59, seen in silhouette
against the starry background.
Here, their combined shape suggests smoke rising from
a pipe, and so the dark nebula's popular name is the Pipe Nebula.
This gorgeous
and expansive view was recorded in
very dark skies over
Hakos,
Namibia.
It covers a full 10 by 7 degree field in the
pronounceable
constellation Ophiuchus.
APOD: 2006 June 19 - Bright Star Regulus near the Leo 1 Dwarf Galaxy
Explanation:
The star on the upper left is so bright it is sometimes hard to
notice the galaxy on the lower right.
Both the star,
Regulus, and the galaxy,
Leo I,
can be found within one degree of each other toward the constellation of Leo.
Regulus is part of a
multiple star system, with a close companion
double star
visible to the upper right of the young
main sequence star.
Leo I is a
dwarf spheroidal galaxy in the
Local Group of galaxies dominated by our
Milky Way Galaxy and
M31.
Leo I is thought to be the most distant of
the several known small satellite galaxies orbiting our
Milky Way Galaxy.
Regulus is located about 75
light years away, in contrast to Leo 1 which is located about 800,000 light years away.
APOD: 2006 June 12 - Edge On Galaxy NGC 5866
Explanation:
Why is this galaxy so thin?
Many disk galaxies are actually just as thin as NGC 5866,
pictured above, but are not
seen edge-on from our vantage point.
One galaxy that is situated edge-on is our own
Milky Way Galaxy.
Classified as a
lenticular galaxy, NGC 5866
has numerous and complex dust lanes appearing dark and red,
while many of the bright stars in the disk give it a more blue underlying hue.
The blue disk of young stars can be seen extending past the
dust in the extremely thin galactic plane,
while the bulge in the disk center appears tinged more orange from the
older and redder stars that likely exist there.
Although similar in mass to our Milky Way Galaxy, light takes about 60,000
years to cross
NGC 5866, about 30 percent less than light takes to cross our own Galaxy.
In general, many disk galaxies are very thin because the gas that
formed them collided with itself as it rotated about the gravitational center.
Galaxy NGC 5866
lies about 44 million light years distant toward the constellation of the Dragon
(Draco).
APOD: 2006 June 9 - Infrared Andromeda
Explanation:
This wide, detailed
Spitzer Space Telescope view
features infrared light from dust (red) and old stars (blue)
in Andromeda, a massive spiral galaxy
a mere 2.5 million light-years away.
In fact, with over twice the diameter of
our own Milky Way,
Andromeda is
the largest nearby galaxy.
Andromeda's population of bright young stars define its sweeping
spiral arms in
visible light images, but here
the infrared view clearly follows the lumpy dust lanes heated by
the young stars as they wind even closer to the
galaxy's core.
Constructed to explore Andromeda's
infrared brightness and
stellar populations, the full mosaic image is composed of
about 3,000 individual frames.
Two smaller companion galaxies,
NGC 205 (below) and
M32 (above)
are also included in the combined fields.
The data confirm that Andromeda (aka M31) houses around 1
trillion
stars, compared
to
4 hundred
billion
for the Milky Way.
APOD: 2006 May 31 - Simulated Gamma ray Sky
Explanation:
Scheduled for launch in 2007, the
Gamma-ray Large Area Space
Telescope (GLAST) will explore the Universe in
gamma-rays, the most energetic form of light.
To get ready, consider this dynamic gamma-ray sky animation -
constructed from simulating the first 55 days (seen above at
one frame per day) of GLAST observations of cosmic gamma-ray sources.
The all-sky view is projected in an astronomical (RA-Dec)
coordinate
system that shows the plane of our Milky Way Galaxy as a
broad U-shape, with the center of the galaxy toward the right.
So what shines in this
gamma-ray sky?
Besides the diffuse Milky Way glow, astronomers testing their
skills on the simulated data have found flaring
active galaxies,
pulsars,
gamma-ray
bursts, the
flaring
Sun, and of course, the
gamma-ray Moon.
APOD: 2006 May 11 - Comet Meets Ring Nebula: Part I
Explanation:
As dawn approached on May 8, astronomer Stefan Seip carefully
watched Fragment C of
broken comet
73P/Schwassmann-Wachmann 3 approach
M57 -
the Ring Nebula, and faint spiral galaxy
IC 1296.
Of course, even though the trio seemed to come close together
in a truly cosmic photo opportunity,
the comet is
in the inner part of our solar system, a mere 0.5
light-minutes
or so from Seip's telescope located near Stuttgart, Germany,
planet Earth.
The Ring Nebula (upper right) is more like 2,000 light-years distant,
well within our own Milky Way Galaxy.
At a distance of 200 million light-years, IC 1296 (between comet
and ring) is beyond even the Milky Way's boundaries.
Because the comet is so close, it appears to move relatively rapidly
against the distant stars.
This dramatic telescopic view was composited from two
sets of images;
one compensating for the comet's apparent
motion and one recording the background stars
and nebulae.
APOD: 2006 May 10 - The Large Cloud of Magellan
Explanation:
Portuguese navigator
Fernando
de Magellan and his crew had plenty of time to study the
southern sky during the first circumnavigation of planet Earth.
As a result, two fuzzy cloud-like
objects easily visible for southern hemisphere
skygazers are known as the
Clouds of Magellan.
Of course, these star clouds are now understood to be
dwarf irregular galaxies, satellites of our larger spiral
Milky Way galaxy.
The Large
Magellanic Cloud (LMC)
pictured above is only about 180,000 light-years distant in
the constellation
Dorado.
Spanning about 15,000 light-years or so, it is
the most massive of the
Milky Way's satellite galaxies
and is the site of the
closest
supernova in modern times.
The prominent red knot on the left is 30 Doradus, or the
Tarantula Nebula, a giant star-forming
region in the
Large
Magellanic Cloud.
APOD: 2006 April 24 - Star Clouds over Arizona
Explanation:
The clouds in the foreground are much different than the clouds in the background.
In the foreground are a photogenic deck of Earth-based
water clouds.
The long exposure used to create the
above photograph
makes the light from the left, reflected from
Phoenix,
Arizona,
USA,
appear like a sunset.
Far in the distance, however, are star clouds from the disk of our
Milky Way Galaxy.
Billions of stars like our Sun live there, circling our Galactic center every 200 million years.
Contrast between the water clouds and the star clouds has been
digitally enhanced.
Between the two, visible on the upper right, is the
planet Jupiter.
APOD: 2006 January 13 - Stars of the Galactic Center
Explanation:
The center
of our Milky Way Galaxy
is hidden
from the prying eyes of optical telescopes by clouds of
obscuring dust and gas.
But in this stunning vista,
the Spitzer Space Telescope's
infrared cameras, penetrate
much of the dust revealing
the stars of the crowded galactic center region.
A mosaic of many smaller snapshots, the detailed,
false-color image shows
older, cool stars in bluish hues.
Reddish glowing dust clouds are associated with
young, hot stars in stellar nurseries.
The galactic center
lies some 26,000 light-years away, toward the constellation
Sagittarius.
At that distance, this picture spans about 900 light-years.
APOD: 2005 December 22 - Andromeda Island Universe
Explanation:
The most distant object easily visible to the unaided eye is
M31,
the great
Andromeda Galaxy
some two million light-years away.
But without a telescope, even this immense spiral galaxy - spanning over
200,000 light years - appears as a
faint, nebulous cloud in the
constellation
Andromeda.
In contrast, a bright yellow nucleus, dark winding dust lanes,
gorgeous blue spiral arms and star clusters are recorded in this
stunning
telescopic
digital mosaic with a cumulative exposure of over 90 hours.
While even casual
skygazers
are now inspired by the knowledge that there are
many distant galaxies like M31, astronomers
seriously debated
this fundamental concept only 80 years ago.
Were these "spiral nebulae" simply outlying components of our own
Milky Way Galaxy or were they instead "island universes" -- distant
systems of stars comparable to the Milky Way itself?
This question was central to the famous
Shapley-Curtis
debate
of 1920, which was later resolved by
observations of M31
in favor of Andromeda,
island
universe.
APOD: 2005 December 16 - GLIMPSE the Milky Way
Explanation:
Scroll right and gaze through the dusty plane of our
Milky Way Galaxy in
infrared light.
The cosmic panorama
is courtesy of the
Galactic Legacy Infrared Mid-Plane Survey Extraordinaire
(GLIMPSE)
project and the
Spitzer
Space Telescope.
The galactic
plane itself runs through the middle
of the false-color view that spans nine degrees
(about 18 full moons)
across the southern constellation Norma.
Spitzer's infrared cameras see through much of the galaxy's
obscuring dust revealing many new star clusters as well as
star forming regions (bright white splotches) and hot
interstellar
hydrogen gas (greenish wisps).
The pervasive red clouds are emission from dust and
organic molecules,
pocked with holes and bubbles blown by
energetic outflows from
massive stars.
Intensely dark patches are regions of dust too dense
for even Spitzer's
infrared vision
to penetrate.
APOD: 2005 October 23 - At the Center of the Milky Way
Explanation:
At the center of our
Milky
Way Galaxy lies a black hole with
over 2 million times the mass of the Sun.
Once a controversial claim, this
astounding conclusion
is now virtually inescapable and based on observations of
stars orbiting
very near the galactic center.
Using one of the Paranal
Observatory's very large telescopes
and a sophisticated infrared camera,
astronomers
patiently followed the orbit of a particular star,
designated S2, as it came within about
17
light-hours of the center of the Milky Way
(about 3 times the radius of Pluto's orbit).
Their results
convincingly show that S2 is moving
under the influence of the enormous gravity of an
unseen object that must be extremely compact -- a
supermassive black hole.
This deep near-infrared
image shows the crowded inner 2
light-years of the Milky Way with the exact position of the
galactic center indicated by arrows.
The ability to track stars so close to the
galactic center
can accurately
measure the black hole's mass and perhaps
even provide an unprecedented test of Einstein's
theory of gravity
as astronomers watch a star orbit a
supermassive black hole.
APOD: 2005 October 4 - The Milky Way in Stars and Dust
Explanation:
The disk of our Milky Way Galaxy is home to hot nebulae, cold dust, and billions of stars.
This disk can be seen from a dark location on Earth as a
band of diffuse light
across the sky.
This band crosses the sky in dramatic fashion in the
above series of wide angle sky exposures from
Chile.
The deepness of the exposures also brings to light a vast network of complex
dust filaments.
Dust is so plentiful that it obscures our
Galaxy's center in visible light,
hiding its true direction until
discovered by other means early last century.
The Galactic Center, though, is
visible above as the thickest part of the disk.
The diffuse glow comes from billions of older, fainter stars like
our Sun,
which are typically much older than the dust or any of the nebulae.
One particularly photogenic area of darkness is the
Pipe Nebula visible above the Galactic Center.
Dark dust is not the
dark matter than dominates our Galaxy -- that
dark matter remains in a form
yet unknown.
APOD: 2005 September 29 - An Unexplored Nebula
Explanation:
The combined light of the
stars
of the Milky Way are
reflected by this cosmic dust cloud that soars
some 300 light-years above the plane of our Galaxy.
Dubbed the
Angel
Nebula by astronomer Steve Mandel's 13 year old
son, the dusty apparition is part of an expansive complex
of dim and relatively unexplored diffuse nebulae,
traced over
large regions seen toward the North and South
Galactic poles.
Along with the blue tint characteristic of more commonly
observed
reflection nebulae,
the Angel Nebula and other dusty
galactic cirrus
also produce a faint reddish luminescence, as
dust grains convert
the Milky Way's
invisible
ultraviolet radiation to visible red light.
Spanning 3x4 degrees on the sky in the constellation Ursa Major,
this wide-angle, high-resolution image was recorded as part of the
Unexplored
Nebula Project.
APOD: 2005 August 25 - Barred Spiral Milky Way
Explanation:
A recent survey of stars
conducted with the Spitzer
Space Telescope is convincing astronomers that our
Milky Way Galaxy is not just your ordinary
spiral galaxy anymore.
Looking out from within
the Galaxy's disk, the true structure of
the
Milky Way is difficult to discern.
However, the penetrating infrared
census of about 30 million stars indicates that the Galaxy is
distinguished by a very large central bar some 27,000 light-years long.
In fact, from a vantage point that viewed our galaxy face-on,
astronomers in distant galaxies
would likely see a striking barred
spiral galaxy suggested
in this artist's illustration.
While previous investigations have
identified
a small central
barred structure, the new results indicate that the Milky Way's
large bar would make about a 45 degree angle with a line
joining the Sun and the Galaxy's center.
DON'T PANIC ...
astronomers still
place the Sun beyond the central
bar region, about a third of the way in from
the Milky Way's
outer edge.
APOD: 2005 August 15 - Perseid Meteors and the Milky Way
Explanation:
Where will the next Perseid meteor appear?
Sky enthusiasts who trekked outside for the
Perseid meteor shower that peaked over the past few days
typically had this question on their mind.
The above movie, where the time-line has been digitally altered, captures part of that very mystery.
Eight meteors from the night of August 12 and
the morning of
August 13 have been identified in the movie so far, seven of which are
Perseids.
Can you identify the non-Perseid meteor?
Since all Perseid meteors appear to come from the
constellation of Perseus, the non-Perseid meteor is the one that streaks
in a different direction.
Early reports are that
this year's Perseids were unfortunately a bit disappointing.
The above digital mosaic was taken from
Alsace,
France, with the photogenic
band of our
Milky Way Galaxy far in the background.
APOD: 2005 June 18 - Visitors Galaxy Gallery
Explanation:
A tantalizing assortment of
island universes is assembled here.
From top left to bottom right are the lovely but distant galaxies
M61,
NGC 4449,
NGC 4725,
NGC 5068,
NGC 5247,
and
NGC
5775/5774.
Most are spiral galaxies
more or less like our own
Milky Way.
The color images reveal distinct pink patches marking the glowing
hydrogen gas clouds in star forming regions along the graceful
spiral arms.
While Virgo cluster galaxy
M61 is perhaps the most striking of these spirals,
the interesting
galaxy pair
NGC 5775/5774 neatly contrasts the characteristic
spiral edge-on and face-on appearance.
The one exception
to
this parade of photogenic spiral galaxies is
the small and relatively close irregular galaxy NGC 4449 (top middle).
Similar to the Large
Magellanic Cloud, companion galaxy to the
Milky Way, NGC 4449 also sports young blue star clusters and
pink star forming regions.
All the
galaxies
in this gallery were imaged with a small
(16 inch diameter) reflecting telescope
and digital camera by public participants in the
Kitt Peak National Observatory
Visitor Center's Advanced Observing Program.
APOD: 2005 June 17 - The Small Cloud of Magellan
Explanation:
Portuguese navigator
Ferdinand Magellan
and his crew had plenty
of time to study the southern sky during the
first circumnavigation of planet Earth.
As a result, two celestial wonders
easily visible for southern hemisphere skygazers
are known as the Clouds of Magellan.
These cosmic clouds are now understood to be dwarf
irregular galaxies,
satellites of our larger spiral
Milky Way Galaxy.
The Small
Magellanic Cloud
pictured above actually spans 15,000 light-years or so
and contains several hundred million stars.
About 210,000 light-years distant in
the constellation
Tucana,
it is the fourth closest of the Milky Way's
known satellite galaxies, after the
Canis Major
and
Sagittarius
Dwarf galaxies and the
Large
Magellanic Cloud.
This gorgeous
view also includes two foreground globular
star clusters NGC 362 (top left) and 47 Tucanae.
Spectacular 47 Tucanae
is a mere 13,000 light-years away and seen here to the right of the
Small Magellanic Cloud.
APOD: 2005 June 5 - A Milky Way Band
Explanation:
Most bright stars in our
Milky Way Galaxy reside in a disk.
Since our Sun also resides in this disk, these stars
appear to us as a
diffuse band that circles the sky.
The above panorama of a
northern band of the
Milky Way's disk covers 90 degrees and is a
digitally created mosaic of several independent exposures.
Scrolling right will display the rest of this spectacular picture.
Visible are many
bright stars,
dark dust lanes,
red emission nebulae,
blue reflection nebulae, and
clusters of stars.
In addition to all this matter that we can see,
astronomers suspect there exists even more
dark matter that we cannot see.
APOD: 2005 May 29 - The Sagittarius Dwarf Tidal Stream
Explanation:
Is our Milky Way Galaxy out to lunch?
Recent wide field images and analyses now indicate that our
home galaxy
is actually still in the process of devouring one of its closer
satellite neighbors.
This unfortunate
neighbor, the
Sagittarius Dwarf galaxy, is now seen to be part of a larger
Sagittarius Tidal Stream,
a loose filament of stars, gas, and possibly dark matter
that entangles the Milky Way.
An artist's depiction of the stream is shown above.
Speculation also holds that the
Sagittarius Dwarf was once pulled through the
Milky Way disk very close to our
Sun's current location.
An important resulting realization is that
galaxies
contain a jumble of clumps and
filaments of both dim and
dark matter.
APOD: 2005 May 8 - CMBR Dipole: Speeding Through the Universe
Explanation:
Our Earth is not at rest.
The Earth moves around the Sun.
The Sun orbits the center of the
Milky Way Galaxy.
The Milky Way Galaxy orbits in the
Local Group of Galaxies.
The Local Group falls toward the
Virgo Cluster of Galaxies.
But these speeds are less than the speed that
all of these objects together move relative to the
cosmic microwave background radiation (CMBR).
In the
above all-sky map, radiation in the
Earth's direction of motion appears
blueshifted and hence hotter,
while radiation on the opposite side of the sky is
redshifted and colder.
The map indicates that the
Local Group moves at about 600 kilometers per second relative to this
primordial radiation.
This high speed was initially unexpected and its
magnitude is still unexplained.
Why are we moving so fast?
What is out there?
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 January 4 - Milky Way Illustrated
Explanation:
What does our Milky Way Galaxy look like from afar?
Since we are stuck inside, and since opaque
dust truncates our view in
visible light, nobody knows for sure.
Drawn above, however, is a good guess based on many different types of observations.
In the Milky Way's center
is a very bright core region centered on a
large black hole.
The Milky Way's bright
central bulge
is now thought to be an
asymmetrical bar
of relatively old and red stars.
The outer regions are where the
spiral arms
are found, dominated in appearance by
open clusters
of young, bright, blue stars, by red
emission nebula, and by dark dust.
The spiral arms reside in a disk dominated in mass by relatively dim stars and
loose gas composed mostly of
hydrogen.
What is not depicted is a huge spherical halo of invisible
dark matter that dominates the mass of the
Milky Way
as well as the motions of stars away from the center.
APOD: 2004 December 27 - Andromeda's Core
Explanation:
The center of the Andromeda galaxy is beautiful but strange.
Andromeda,
indexed as M31, is so close to our own
Milky Way Galaxy that it
gives a unique perspective into galaxy composition by
allowing us to see into its core.
Billions of stars swarm around a center that has
two nuclei and likely houses a
supermassive black hole
over 5 million times the mass of our
Sun.
M31 is about two million light years away and
visible with the unaided eye towards the constellation of Andromeda, the princess.
Pictured above, dark
knots of
dust are seen superposed on the inner 10,000
light years of M31's core.
The brighter stars are foreground stars located in our
Milky Way Galaxy.
APOD: 2004 December 14 - Nearby Spiral M33
Explanation:
Spiral galaxy M33 is a mid-sized member of our
Local Group of Galaxies.
M33 is also called the
Triangulum Galaxy for the constellation in which it resides.
About four times smaller (in radius) than our
Milky Way Galaxy
and the Andromeda Galaxy (M31),
it is much larger than the many of the local
dwarf spheroidal galaxies.
M33's proximity to
M31 causes it to be
thought by some to be a satellite galaxy
of this more massive galaxy.
M33's proximity to our
Milky Way Galaxy
causes it to appear more than twice the angular size of the
Full Moon, and be
visible with a good pair of binoculars.
APOD: 2004 November 6 - X-Rays from the Galactic Core
Explanation:
Using the orbiting
Chandra
X-ray Observatory, astronomers have taken
this long look at the core of our
Milky Way galaxy, some 26,000 light-years away.
The spectacular false-color view spans about 130 light-years.
It reveals an energetic region
rich in x-ray sources and high-lighted by the
central source, Sagittarius A*, known
to be a supermassive black hole
with 3 million times the
mass of
the Sun.
Given its tremendous mass, Sagittarius A* is amazingly faint in x-rays
in comparison to central black holes observed in
distant galaxies,
even during its frequent x-ray flares.
This suggests that this supermassive black hole has been
starved
by a lack of infalling material.
In fact, the sharp Chandra image shows clouds of multi-million
degree gas dozens of light-years across flanking
(upper right and lower left) the
central
region -- evidence that violent events have
cleared much material from
the vicinity of the black hole.
APOD: 2004 October 14 - Glimpse of a Globular Star Cluster
Explanation:
Not a glimpse of
this cluster of stars
can be seen
in the inset visible light image (lower right).
Still,
the infrared view
from the Spitzer
Space Telescope reveals
a massive globular star cluster of about 300,000 suns in
an apparently empty region of sky in the constellation Aquila.
When astronomers used
infrared cameras to peer
through obscuring dust in the plane of our
Milky Way galaxy,
they were rewarded with the surprise discovery of the
star cluster, likely one of the last such
star clusters
to be found.
Globular star clusters normally
roam
the halo of the Milky Way,
ancient relics
of our galaxy's formative years.
Yet the Spitzer image shows this otherwise hidden cluster
crossing through
the middle of the galactic plane some 10,000 light-years away.
At that distance, the picture spans only about 20 light-years.
In the false color infrared image, the red streak is a dust cloud
which seems to lie behind the cluster core.
APOD: 2004 September 23 - La Silla's Starry Night
Explanation:
On clear, moonless nights, the stars still come out with a
vengance above the high-altitude
La Silla
astronomical observatory.
Taking advantage of a recent visit to this first
European Southern Observatory
(ESO) site
constructed
on a mountain top in Chile, ESO software engineer Nico Housen
recorded this stunning sky view.
Difficult to see from
light polluted areas,
faint stars and dark
dust clouds along the plane of our
Milky Way Galaxy arc across
the gorgeous photo.
In the foreground lies the highly polished 15-meter diameter dish
antenna of the Swedish-ESO
Submillimeter Telescope
(now decommissioned).
Beyond it, silhouetted by starlight, is
the dome of one of La Silla's large optical instruments, a
3.6 meter
telescope.
Dramatically
reflected in the
focusing, mirror-like surface of
the dish, the vista behind the photographer
appears inverted,
with the dark horizon hanging above the Milky Way and
the starry night.
APOD: 2004 September 2 - The Large Cloud of Magellan
Explanation:
Portuguese navigator
Fernando
de Magellan and his crew had plenty
of time to study the southern sky during the
first circumnavigation of planet Earth.
As a result, two fuzzy cloud-like
objects easily visible for southern hemisphere skygazers
are known as the
Clouds of Magellan.
Of course, these star clouds are now understood to be dwarf
irregular galaxies,
satellites of our larger spiral
Milky Way galaxy.
The Large
Magellanic Cloud (LMC)
pictured above is only about 180,000 light-years distant in
the constellation
Dorado.
Spanning about 15,000 light-years or so, it is
the most massive of the Milky Way's satellite galaxies
and is the site of the
closest
supernova in modern times.
The prominent red knot on the right is 30 Doradus, or the
Tarantula Nebula, a giant star-forming
region in the
Large Magellanic Cloud.
APOD: 2004 July 1 - NGC 7331: A Galaxy So Inclined
Explanation:
If our own Milky Way
galaxy
were 50 million light-years
away with its disk inclined slightly to our line of sight, it
would look a lot like large
spiral
galaxy NGC 7331.
In fact, seen here in a
false-color infrared image from
the Spitzer Space Telescope,
NGC 7331 is interesting in
part because it is thought to be so similar to the
Milky Way.
Light from older, cooler stars, shown in blue, dominates the
central bulge of
NGC 7331, while Spitzer data also indicates the
presence of a black hole within this galaxy's central regions -
about the same size as the black hole at
our own galactic core.
Shown in red and brown, radiation from complex molecules associated
with dust traces NGC 7331's star forming spiral arms.
The arms span around 100,000 light-years,
about
the size of the Milky Way.
Curiously, a further
star forming ring is visible in yellowish hues,
20,000 light-years or so from the center of NGC 7331,
but it is not known if such a
structure
exists within our own galaxy.
APOD: 2004 February 28 - POX 186: Not So Long Ago
Explanation:
Not so long ago and not so far, far away, a
galaxy
was born.
Seen in this Hubble Space Telescope image, the
island universe of
stars, gas, and dust cataloged as POX 186 is a mere 68 million
light-years distant toward an uncrowded region in the
constellation Virgo.
POX 186 is truly dwarfed by
galaxies like our own Milky Way.
The diminutive galaxy is about 900 light-years across with around 10
million stars, compared to the
Milky
Way's 100,000 light-year span and
more than 200 billion stars.
Cosmically speaking, POX 186 is
also very young as the Hubble snapshot
reveals a disturbed galaxy that is likely
the result of a 100 million
year old collision between two even smaller
star systems.
In fact,
POX 186 observations
suggest that such isolated, small
galaxies may be the last to form, since the most massive
galaxies
in the universe seem to have formed billions of years ago.
APOD: 2004 February 23 - Heaven on Earth
Explanation:
If sometimes it appears that the entire
Milky Way Galaxy
is raining down on your head, do not despair.
It happens twice a day.
As the Sun rises in the East,
wonders of the night sky
become less bright than the
sunlight scattered by our own
Earth's atmosphere, and so fade from view.
They will only rotate
back into view when the Earth again eclipses our bright Sun at dusk.
This battle between heaven and Earth was
captured dramatically in a digitally enhanced double-exposure over the
Kofa
Mountains in
Arizona,
USA in 2003 May.
Dark dust,
millions of stars, and bright
glowing red gas highlight the
plane of our
Milky Way Galaxy,
which lies on average thousands of
light years behind
Earth's mountains.
APOD: 2003 November 17 - Canis Major Dwarf: A New Closest Galaxy
Explanation:
What is the closest galaxy to the Milky Way?
The new answer to this old question is the
Canis Major dwarf galaxy.
For many years astronomers thought the
Large Magellan Cloud
(LMC) was closest, but its title was supplanted in 1994 by the
Sagittarius dwarf galaxy.
Recent measurements indicate that the Canis Major dwarf is only 42,000 light years from the
Galactic center,
about three quarters of the distance to the
Sagittarius dwarf
and a quarter of the distance to the LMC.
The discovery was made in data from the
2MASS-sky survey, where infrared light allows a better view through our optically opaque
Galactic plane.
The labeled illustration above shows the location
of the newly discovered Canis Major dwarf and its associated
tidal stream of material in relation to our
Milky Way Galaxy.
The Canis Major dwarf and other
satellite galaxies are slowly being
gravitationally ripped apart as they
travel around and through our Galaxy.
APOD: 2003 September 30 - The Sagittarius Dwarf Tidal Stream
Explanation:
Is our Milky Way Galaxy out to lunch?
Recent wide field images and analyses now indicate that our
home galaxy
is actually still in the process of devouring its closest
satellite neighbor.
This unfortunate
neighbor, the
Sagittarius Dwarf galaxy, is now seen to be part of a larger
Sagittarius Tidal Stream,
a loose filament of stars, gas, and possibly dark matter
that entangles the Milky Way.
An artist's depiction of the stream is shown above.
Speculation also holds that the
Sagittarius Dwarf was once pulled through the
Milky Way disk
very close to our
Sun's current location.
An important resulting realization is that
galaxies
contain a jumble of clumps and
filaments of both
dim and
dark matter.
APOD: 2003 September 28 - Our Galaxy in Stars, Gas, and Dust
Explanation:
The disk of our
Milky
Way Galaxy is home to hot nebulae,
cold dust, and billions of stars.
The red nebulae visible in the above contrast-enhanced picture are primarily
emission nebulae, glowing clouds of
hydrogen
gas heated by nearby, bright, young stars.
The blue nebulae are primarily
reflection nebulae,
clouds of gas and fine dust reflecting the light of
nearby bright stars.
Perhaps the most striking, though, are the areas of darkness,
including the Pipe Nebula
visible on the image top left.
These are lanes of thick dust,
many times containing relatively cold
molecular clouds of gas.
Dust is so plentiful that it obscures the
Galactic Center in visible light,
hiding its true direction until discovered
early
last century.
The diffuse glow comes from
billions of older,
fainter stars like our
Sun,
which are typically much older than any of the nebulae.
Most of the mass of
our
Galaxy remains in a form currently
unknown.
APOD: 2003 September 24 - M33: Spiral Galaxy in Triangulum
Explanation:
The small constellation
Triangulum
in the northern sky harbors
this magnificent face-on spiral galaxy, M33.
Its popular names include the Pinwheel Galaxy or just
the Triangulum Galaxy.
M33's diameter spans over 50,000 light-years, making it third largest in
the Local
Group of galaxies after the Andromeda Galaxy (M31), and our
own Milky Way.
About 3 million light-years from the Milky Way, M33
lies very close to the Andromeda Galaxy and
observers
in these two galaxies would likely have spectacular views of
each other's grand spiral star systems.
As for the view from planet Earth, this
sharp
27 frame mosaic of M33 nicely shows off blue star clusters
and pinkish star forming regions which trace the galaxy's
loosely wound spiral arms.
In fact, the cavernous NGC 604 is the brightest
star forming region seen here, visible
along an arm arcing above and to the right
of the galaxy center.
Like M31, M33's population of well-measured variable stars
have helped make this nearby spiral a
cosmic
yardstick for
establishing
the distance scale of the Universe.
APOD: 2003 September 9 - A Gemini Sky
Explanation:
Where will Gemini take us tonight?
It is dusk and Gemini North,
one of the largest telescopes on
planet Earth,
prepares to peer into the distant universe.
Gemini's flexible 8.1-mirror
has taken already effectively taken humanity to
distant stars,
nebulas,
galaxies, and
quasars, telling us about the geometry,
composition, and evolution of our universe.
The above picture is actually a composite of over
40 images taken while the Gemini dome rotated,
later adding an image of the star field taken
from the same location.
The Gemini dome is not transparent -- it only appears so
because it rotated during the exposures of this image.
The constellations of
Scorpius and Sagittarius can be seen above the dome, as well as the
sweeping band of our
Milky Way Galaxy,
including the direction toward the
Galactic center.
Gemini North's twin,
Gemini South,
resides in Cerro Pachn,
Chile.
This night, 2003 August 19,
Gemini North
took us only into the outer
Solar System,
observing
Pluto
in an effort to better determine the composition of its
thin atmosphere.
APOD: 2003 August 25 - The Northern Milky Way
Explanation:
Many of the stars in our home
Milky Way Galaxy appear together as a dim band
on the sky that passes nearly over the Earth's
north and south poles.
Pictured above is the part of
our Galaxy that passes
closest over the north pole.
Placing your cursor over the image will bring up the names of several constellations and
bright stars.
The diffuse white Galaxy glow is created by billions of stars,
while red patches are large
emission nebulas,
usually marking areas where bright stars have recently formed.
In the north, all of the
lights visible at night and all lights that created
this image were emitted within the past few thousand years
from within the Milky Way Galaxy -- except one.
On the upper right is a small faint patch designated M31, the
Andromeda Galaxy.
M31 is a spiral galaxy similar to our
Milky Way but so distant it emits the oldest light distinguishable by the unaided eye --
light that takes over two million years to reach us.
APOD: 2003 August 2 - Island Universe, Cosmic Sand
Explanation:
On August 13, 2002,
while counting
Perseid meteors under
dark, early morning Arizona skies,
Rick Scott set out to photograph their fleeting
but fiery trails.
The equipment he used included a telephoto lens and fast
color film.
After 21 pictures he'd caught only two meteors, but luckily
this was one of them.
Tracking the sky, his ten minute long exposure shows a
field of many stars in our own Milky Way galaxy, most too
faint to be seen by the unaided eye.
Flashing
from lower left to upper right, the bright meteor would
have been an easy eyeful though,
as friction with Earth's atmosphere
vaporized the hurtling grain of
cosmic sand, a piece of dust from Comet
Swift-Tuttle.
Just above and left of center, well beyond the stars of
the Milky Way, lies the island universe
known as M31 or the Andromeda galaxy.
The visible meteor trail begins about 100 kilometers
above Earth's surface, one of the closest celestial objects
seen in the sky.
In contrast, Andromeda, about 2 million light-years
away, is the most distant object easily visible to the naked-eye.
APOD: 2003 July 12 - X-Ray Milky Way
Explanation:
If you had x-ray vision,
the center regions
of our Galaxy would not be hidden from
view by the immense cosmic dust clouds
opaque to visible light.
Instead,
the Milky Way
toward Sagittarius might look something
like this stunning mosaic
of images from the orbiting
Chandra Observatory.
Pleasing to look at, the gorgeous false-color
representation of
the x-ray data shows
high energy x-rays in blue, medium energies in green,
and low energies in red.
Hundreds of white dwarf stars,
neutron stars, and black holes immersed in a
fog of multimillion-degree gas are included in the
x-ray vista.
Within the white patch at the image center lies
the Galaxy's central supermassive black hole.
Chandra's sharp
x-ray vision will likely lead to a new
appreciation of our Milky Way's most active neighborhood
and has already indicated that the hot gas itself may
have a temperature of a mere 10 million degrees Celsius
instead of 100 million degrees as previously thought.
The full mosaic is composed of 30 separate images and covers
a 900 by 400 light-year swath
at
the galactic center.
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 June 3 - The Milky Way Behind an Eclipsed Moon
Explanation:
What's behind the Moon? Each month,
our Moon passes in front of --
and outshines -- many an interesting star field.
Exceptions occur during a
new Moon and during a
total eclipse.
In the background of a new
Moon
is usually the Sun, an even brighter orb that even
more easily outshines everything behind it, except during a
total solar eclipse.
Even the longest total solar eclipse
lasts just a few minutes, while the
Sun's corona still remains bright.
During a total lunar eclipse,
however, the full Moon
dims and a majestic star field may present itself for an hour or more.
Such was the case during the middle of last month,
when a rare glimpse of an eclipsed Moon superposed in front of the disk of our home
Milky Way Galaxy was captured.
Although fully in the Earth's shadow, the eclipsed Moon is still the
brightest object on the right.
The above image was captured during sub-zero weather from the
Teide 2003 expedition to
Mirador del Pico Viejo, a mountain in the
Canary Islands,
Spain, off the northwest coast of
Africa.
APOD: 2003 February 9 - COBE Dipole: Speeding Through the Universe
Explanation:
Our
Earth is not at rest.
The Earth moves around the
Sun.
The Sun orbits the center of the
Milky Way Galaxy.
The Milky Way Galaxy orbits in the
Local Group of Galaxies.
The Local Group falls toward the
Virgo Cluster of Galaxies.
But these speeds are less than the speed that
all of these objects together move relative to the
cosmic microwave background (CMB).
In the
above all-sky map, radiation in the
Earth's direction of motion appears
blueshifted and hence hotter,
while radiation on the opposite side of the sky is
redshifted and colder.
The map indicates that the
Local Group moves at about 600 kilometers per
second relative to this
primordial radiation.
This high speed was initially unexpected and its
magnitude is still unexplained.
Why are we moving so fast?
What is out there?
APOD: 2003 January 25 - Palomar 13's Last Stand
Explanation:
Globular star cluster
Palomar 13
has roamed the halo of our
Milky Way Galaxy for the last 12 billion years.
The apparently
sparse
cluster of stars just left of center in
this composite color digital image,
it is one of the smallest, faintest
globular
clusters known.
(The bright foreground star near bottom
is unrelated and creates the spiky imaging artifacts.)
Observations spanning forty years indicate
that Palomar 13's
galactic halo orbit
is a highly eccentric one which, every one or two billion
years, brings it relatively close to the galactic center.
With each close approach to the
Milky Way's central regions,
gravitational tidal forces
strip away
the delicately bound cluster stars.
In fact, detailed present day studies offer evidence
for a dramatic end to this dwindling cluster's tidal
tug of war.
Palomar 13's latest close approach was only
about 70 million years ago.
But, when Palomar 13 again approaches the galaxy, it
could well turn out to be
the cluster's
last stand.
APOD: 2003 January 8 - X-Rays from the Galactic Core
Explanation:
Using the orbiting
Chandra
X-ray Observatory, astronomers have taken
this long look at the core of our
Milky Way galaxy, some 26,000 light-years away.
The spectacular false-color view spans about 130 light-years.
It reveals an energetic region
rich in x-ray sources and
high-lighted by the
central source, Sagittarius A*, known
to be a supermassive black hole
with 3 million times the
mass of
the Sun.
Given its tremendous mass, Sagittarius A* is amazingly faint in x-rays
in comparison to central black holes observed in
distant galaxies,
even during its frequent x-ray flares.
This suggests that this supermassive black hole has been
starved
by a lack of infalling material.
In fact, the sharp Chandra image shows clouds of multi-million
degree gas dozens of light-years across flanking
(upper right and lower left) the
central
region -- evidence that violent events have
cleared much material from
the vicinity of the black hole.
APOD: 2003 January 3 - POX 186: Not So Long Ago
Explanation:
Not so long ago and not so far, far away, a
galaxy
was born.
Seen in this Hubble Space Telescope image, the
island universe of
stars, gas, and dust cataloged as POX 186 is a mere 68 million
light-years distant toward an uncrowded region in the
constellation Virgo.
POX 186 is truly dwarfed by
galaxies like our own Milky Way.
The diminutive galaxy is about 900 light-years across with around 10
million stars, compared to the Milky Way's 100,000 light-year span and
more than 200 billion stars.
Cosmically speaking, POX 186 is
also very young as the Hubble snapshot
reveals a disturbed galaxy that is likely
the result of a 100 million
year old collision between two even smaller
star systems.
In fact,
POX 186 observations
suggest that such isolated, small
galaxies may be the last to form, since the most massive
galaxies
in the universe seem to have formed billions of years ago.
APOD: 2002 December 29 - NGC 1818: A Young Globular Cluster
Explanation:
Globular clusters once ruled the
Milky Way.
Back in the
old days, back when our Galaxy first
formed, perhaps thousands of globular clusters roamed
our Galaxy.
Today, there are
perhaps 200 left.
Many
globular clusters were destroyed
over the eons by repeated fateful encounters
with each other or the
Galactic center.
Surviving relics are older than any Earth fossil,
older than any
other structures in our Galaxy, and
limit the universe itself in raw age.
There are few, if any, young
globular clusters in our
Milky Way Galaxy because
conditions are not ripe for more to form.
Things are different next door, however, in the neighboring
LMC galaxy.
Pictured above is a "young" globular cluster residing there:
NGC 1818.
Observations show it formed
only about 40 million years ago -
just yesterday compared to the 12 billion year ages of
globular clusters in our own
Milky Way
APOD: 2002 December 2 - Nearby Spiral M33
Explanation:
Spiral galaxy M33 is a mid-sized member of our
Local Group of Galaxies.
M33 is also called the
Triangulum Galaxy for the
constellation in which it resides.
About four times smaller (in radius) than our
Milky Way Galaxy
and the Andromeda Galaxy (M31),
it is much larger than the many of the local
dwarf spheroidal galaxies.
M33's proximity to
M31 causes it to be
thought by some to be a satellite galaxy
of this more massive galaxy.
M33's proximity to our
Milky Way Galaxy
causes it to appear more than twice the angular size of the
Full Moon, and be
visible with a good pair of binoculars.
The
above high-resolution image from the
0.90-m telescope
at Kitt Peak National Observatory is a four-color composite.
APOD: 2002 October 18 - At the Center of the Milk Way
Explanation:
At the center of our
Milky
Way Galaxy lies a black hole with
over 2 million times the mass of the Sun.
Once a controversial claim, this
astounding conclusion
is now virtually inescapable and based on observations of
stars orbiting
very near the galactic center.
Using one of the Paranal
Observatory's very large telescopes
and the sophisticated infrared camera
NACO,
astronomers
patiently followed the orbit of a particular star,
designated S2, as it came within about 17 light-hours of the
center of the Milky Way
(17 light-hours is only about 3 times the radius of Pluto's orbit).
Their
results convincingly show that
S2 is moving
under the influence of the enormous gravity of an
unseen object which must be extremely compact -- a
supermassive black hole.
This deep NACO
near-infrared image shows the crowded inner 2
light-years of the Milky Way with the exact position of the
galactic center indicated by arrows.
NACO's ability to track stars so close to the
galactic center
can accurately
measure the black hole's mass and perhaps
even provide an unprecedented test of Einstein's
theory of gravity
as astronomers watch a star orbit a
supermassive black hole.
APOD: 2002 September 23 - The Milky Way Over the French Alps
Explanation:
Have you ever seen the
band of our
Milky Way Galaxy?
Chances are you have never seen it like this --
nor could you.
In a clear sky from a dark location at the right time, a
faint band of light is visible across the sky.
This band is the disk of our
spiral galaxy.
Since we are inside this disk, the band appears to encircle the Earth.
The above spectacular picture is a bit of a
digital trick, though.
A first shot was taken in July 2000 with the camera
counter-rotating from the Earth
so that the stars appear fixed.
This allowed a long exposure from which a great
amount of detail could emerge from the
background star field.
Later, after moonrise,
a much shorter image was taken from the same location
catching details of the French Alps near
Mount Blanc, the
highest mountain in
Western Europe.
Reflections in the water were later enhanced digitally.
APOD: 2002 August 23 - Island Universe, Cosmic Sand
Explanation:
On August 13,
while counting Perseid meteors under
dark, early morning Arizona skies,
Rick Scott set out to photograph their fleeting
but fiery trails.
The equipment he used included a telephoto lens and fast
color film.
After 21 pictures he'd caught only two meteors, but luckily
this was one of them.
Tracking the sky, his ten minute long exposure shows a
field of many stars in our own Milky Way galaxy, most too
faint to be seen by the unaided eye.
Flashing
from lower left to upper right, the bright meteor would
have been an easy eyeful though,
as friction with Earth's atmosphere
vaporized the hurtling grain of
cosmic sand, a piece of dust from Comet
Swift-Tuttle.
Just above and left of center, well beyond the stars of
the Milky Way, lies the island universe
known as M31 or the Andromeda galaxy.
The visible meteor trail begins about 100 kilometers
above Earth's surface, one of the closest celestial objects
seen in the sky.
In contrast, Andromeda, about 2 million light-years
away, is the most distant object easily visible to the naked-eye.
APOD: 2002 August 3 - The Galactic Center A Radio Mystery
Explanation:
Tuning in
to the center of our Milky Way galaxy,
radio
astronomers explore a complex, mysterious place.
A premier high resolution view,
this startlingly beautiful picture
covers a 4x4 degree region around the galactic center.
It was constructed from 1 meter wavelength radio data
obtained by telescopes of the
Very Large Array near
Socorro, New Mexico, USA.
The
galactic center
itself is at the edge of the extremely
bright object labeled Sagittarius (Sgr) A, suspected of harboring
a million solar mass black hole.
Along the galactic plane which runs diagonally
through the image are tortured clouds of gas energized by
hot stars and bubble-shaped supernova remnants (SNRs)
- hallmarks of
a violent and
energetic cosmic environment.
But perhaps most intriguing are
the arcs, threads, and filaments which
abound in the scene.
Their uncertain origins challenge
present theories of the dynamics of the galactic center.
APOD: 2002 July 19 - Counting Stars in the Infrared Sky
Explanation:
The bulging center of
our Milky Way Galaxy,
dark cosmic clouds, the
thin galactic plane, and even nearby galaxies are easy to spot in this
sky view.
But each pixel in the digital image is actually based on star counts
alone -- as derived from the
Two Micron All Sky Survey
(2MASS) database.
In 2001, the
2MASS project completed a ground-based survey of the
entire sky
and cataloged upwards of 250 million stars.
Their full all-sky picture
assigns a brightness and color to
individual pixels based on corresponding star counts in each of the
survey's three
near-infrared bands.
In this cropped image, the
star-packed galactic center
is toward the
upper left, with the bright plane of our Galaxy running horizontally
through it.
Dense regions of interstellar
dust clouds, still opaque to penetrating
near-infrared light,
appear dark
by reducing the 2MASS
star counts.
Our fuzzy neighboring galaxies, the large and small
Magellanic Clouds,
are at the lower right, while scattered single bright spots
correspond to the intense concentrations of stars in the Milky Way's
large globular star clusters.
APOD: 2002 May 18 - Andromeda Island Universe
Explanation:
How far can you see?
The most distant object easily visible to the unaided eye is
M31,
the great
Andromeda Galaxy
some two million light-years away.
Without a telescope, even this immense spiral galaxy appears
as an unremarkable, faint, nebulous cloud in the
constellation
Andromeda.
But a bright yellow nucleus, dark winding dust lanes, gorgeous blue
spiral arms and star clusters are recorded in this stunning
telescopic digital
mosaic of the nearby island universe.
While even casual
skygazers
are now inspired by the knowledge that there are
many distant galaxies like M31, astronomers
seriously debated
this fundamental concept only 80 years ago.
Were these "spiral nebulae" simply outlying components of our own
Milky Way Galaxy or were they instead "island universes" -- distant
systems of stars comparable to the Milky Way itself?
This question was central to the famous
Shapley-Curtis
debate
of 1920, which was later resolved by
observations of M31
in favor of Andromeda,
island
universe.
APOD: 2002 January 17 - Pick a Galaxy Any Galaxy
Explanation:
Pick a galaxy,
any galaxy.
In the top panel you can
choose from a myriad of
distant galaxies
revealed in a deep Hubble Space Telescope image of a narrow slice of
the cosmos toward the constellation
Hercules.
If you picked the distorted reddish galaxy indicated by the yellow box,
then you've chosen one a team of infrared astronomers has recently
placed at a distance of 9 billion light-years.
Classified as an ERO (Extremely Red Object), this galaxy is
from a time
when the
Universe was only one third its
present age.
Along the bottom panel, this galaxy's
appearance
in filters ranging from visible to infrared
wavelengths
(left to right) is presented as a series of negative images.
The brightness of the galaxy in the infrared compared
to the visible suggests that light from intense star
formation activity, reddened by dust clouds within
the galaxy itself, is responsible for the extremely red color.
Astronomers estimate that this galaxy has around 100 billion stars
and may in fact be a very distant mirror -- an
analog
of our own
Milky Way
Galaxy in its
formative years.
APOD: 2002 January 10 - X-Ray Milky Way
Explanation:
If you had x-ray vision,
the center regions
of our Galaxy would not be hidden from
view by immense cosmic dust clouds
opaque to visible light.
Instead,
the Milky Way
toward Sagittarius might look something
like this stunning mosaic
of images from the orbiting
Chandra Observatory.
Pleasing to look at, the gorgeous false-color
representation of
the x-ray data shows
high energy x-rays in blue, medium energies in green,
and low energies in red.
Hundreds of white dwarf stars,
neutron stars, and black holes immersed in a
fog of multimillion-degree gas are included in the
x-ray vista.
Within the white patch at the image center lies
the Galaxy's central supermassive black hole.
Chandra's sharp
x-ray vision will likely lead to a new
appreciation of our Milky Way's most active neighborhood
and has already indicated that the hot gas itself may
have a temperature of a mere 10 million degrees Celsius
instead of 100 million degrees as previously thought.
The full mosaic is composed of 30 separate images and covers
a 900 by 400 light-year swath
at
the galactic center.
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 September 21 - Where a Black Hole Roams
Explanation:
Black hole candidate XTE J1118+480 is known to roam the halo
of our Milky Way Galaxy.
This exotic
system - thought to be a
stellar mass black hole consuming
matter from a companion star - was discovered only last year as a
flaring celestial x-ray source.
Suggestively termed a
microquasar,
recent radio and archival optical observations of
its
motion through the sky have now allowed its
orbit to be calculated.
Illustrated above, the
black hole's present galactic location is
indicated by the purple dot, with the
Sun's position in yellow.
A mere 6,000 light-years from the Sun now, XTE J1118+480's orbit is
traced by the orange line, backtracked for some 230 million years into
the past based on models of the Galaxy.
Astronomers note this black hole's orbit about the galactic center,
looping high above and below
the Galaxy's
plane of gas, dust,and stars,
is similar to orbits of globular
star clusters,
ancient denizens of our Galaxy.
It seems likely that
XTE J1118+480 too has its origins in the early
history and
halo of the Milky Way.
APOD: 2001 September 17 - Southwest Andromeda
Explanation:
This
new image composite of the southwest region of
M31 from the
Subaru Telescope shows many stars,
nebulae, and star clusters never before resolved.
An older population of stars near
Andromeda's center
causes the yellow hue visible on the upper right.
Young blue stars stand out in the
spiral arms on the lower left.
Red emission nebula,
blue open clusters of stars,
and sweeping lanes of dark
dust punctuate the swirling giant.
Andromeda, at about 2.5 million
light years distant, and our
Milky Way are the largest
galaxies in the
Local Group of Galaxies.
Understanding
M31 helps astronomers to
understand our own
Milky Way Galaxy, since the two are so similar.
APOD: 2001 August 14 - X-Rays from the Galactic Plane
Explanation:
In February 2000, the orbiting
Chandra X-ray Observatory spent 27 hours
staring into the plane
of our Milky Way galaxy.
Its target was a spot in the small
constellation
Scutum, within the Milky Way's
zone of avoidance where galactic
gas and dust clouds block visible light, making a poor
window for optical telescopes.
However the penetrating x-ray observations looked through
the obscurations revealing the Milky Way and the Universe beyond.
The x-ray view is
reconstructed above in false color.
Distant active galaxies
emitting high energy x-rays appear as blue dots,
while reddish dots are sources of lower energy x-rays,
likely stars within the
Milky Way itself.
Intriguing is the
diffuse blue glow of high energy x-rays,
distinct from the individual sources in the picture.
Astronomers have
long debated whether our galactic plane's apparently
extended x-ray emission
was due to discrete sources or diffuse hot gas.
As these results
suggest diffuse interstellar
gas with a temperature of tens of millions of degrees Celsius
is indeed the answer, other questions arise.
What heats the gas to these incredible temperatures?
Why does this energetic gas linger in the galactic plane?
APOD: 2001 August 4 - Neighboring Galaxy: The Large Magellanic Cloud
Explanation:
The brightest galaxy visible from our own Milky Way Galaxy is the
Large Magellanic Cloud (LMC).
Visible predominantly from
Earth's Southern Hemisphere, the
LMC is the second
closest galaxy,
neighbor to the
Small Magellanic Cloud,
and one of
eleven known dwarf galaxies that orbit our Milky Way Galaxy.
The
LMC is an
irregular galaxy composed of a bar of older red stars,
clouds of younger blue stars, and a bright red star forming
region visible near the top of the
above image called the
Tarantula Nebula.
The brightest
supernova of modern times,
SN1987A, occurred in the
LMC.
APOD: 2001 July 30 - Star Cluster R136 Bursts Out
Explanation:
In the center of star-forming region
30 Doradus
lies a huge cluster of the largest, hottest,
most massive stars known.
Known as
R136, the cluster's
energetic stars are breaking out of the
cocoon of gas and dust from which they formed.
This disintegrating cocoon, which fills the rest of the recently released
above picture by the
Hubble Space Telescope,
is predominantly
ionized hydrogen from 30 Doradus.
R136 is composed of thousands of
hot blue stars,
some about 50 times more massive than our
Sun.
R136, also known as
NGC 2070, lies in the
LMC - a satellite galaxy to our own
Milky Way Galaxy.
Although the young ages of stars in R136 make it
similar to a Milky Way
open cluster,
its high density of stars will likely turn it into a low mass
globular cluster
in a few billion years.
APOD: 2001 July 25 - Hot Gas Halo Detected Around Galaxy NGC 4631
Explanation:
Is our Milky Way Galaxy
surrounded by a halo of hot gas?
A step toward solving this long-standing mystery
was taken recently with
Chandra X-ray observations of nearby galaxy
NGC 4631.
In the
above composite picture, newly resolved diffuse
X-ray emission is shown in blue, superposed on an
HST image
showing massive stars in red.
Since NGC 4631 is similar to the
Milky Way, this
observation indicates that our own Galaxy
is indeed surrounded by a halo of hot X-ray emitting gas,
although we are too close to clearly differentiate it from
more nearby extended X-ray sources.
The
clusters of massive stars
probably heat the halo gas.
Exactly how this gas gets ejected into a
halo is a topic of
continuing research.
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 27 - Moonlight, Mars and Milky Way
Explanation:
Aloha
and welcome to a breath-taking skyscape.
In this celestial scene,
a four day old Moon illuminates a dreamlike foreground while
bright planet Mars
(above center) rules and
the
Milky Way's cosmic clouds of stars and dust seem to stretch
from horizon to horizon.
The picture was taken on May 27th from what may be the best
amateur astronomy observing site
on planet Earth, near the
Mauna Kea, Hawai'i
Visitor Center, 9,600 feet above sea level.
Remarkable in the volcanic foreground are moonlit clouds and
an "ahu hoku" - a star marker or star altar - built up of rocks
topped with a white piece of coral gently glowing in the moonlight.
Now near its closest approach in 13 years,
Mars still lingers between the
Milky Way constellations of
Sagittarius and Scorpius.
High above the horizon by midnight,
the Red Planet is
exceptionally well placed for
earthdwellers to admire it.
Astrophotographer
Barney Magrath
comments that this splendid sky view
represents one of the joys of
photography itself.
When making the time exposure he did not realize that the
ahu hoku would become such a beautiful element in his celestial
composition.
APOD: 2001 April 27 - Visitors' Galaxy Gallery
Explanation:
A tantalizing assortment of
island universes is assembled here.
From top left to bottom right are the lovely but distant galaxies
M61,
NGC 4449,
NGC 4725,
NGC 5068,
NGC 5247,
and
NGC
5775/5774.
Most are
spiral galaxies
more or less like
our own Milky Way.
The color images reveal distinct pink patches marking the glowing
hydrogen gas clouds in star forming regions along the graceful
spiral arms.
While Virgo cluster galaxy
M61 is perhaps the most striking of these spirals,
the interesting
galaxy pair
NGC 5775/5774 neatly contrasts the characteristic
spiral edge-on and face-on appearance.
The one exception
to
this parade of photogenic spiral galaxies is
the small and relatively close irregular galaxy NGC 4449 (top middle).
Similar to the Large
Magellanic Cloud, companion galaxy to the
Milky Way, NGC 4449 also sports young blue star clusters and pink star forming
regions.
All the
galaxies
in this gallery were imaged with a small
(16 inch diameter) reflecting telescope
and digital camera by public participants in the
Kitt Peak National Observatory
Visitor Center's Advanced Observing Program.
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 11 - NGC 1818: A Young Globular Cluster
Explanation:
Globular clusters once ruled the
Milky Way.
Back in the
old days, back when our Galaxy first
formed, perhaps thousands of globular clusters roamed
our Galaxy.
Today, there are
perhaps 200 left.
Many
globular clusters were destroyed
over the eons by repeated fateful encounters
with each other or the
Galactic center.
Surviving relics are older than any Earth fossil,
older than any
other structures in our Galaxy, and
limit the universe itself in raw age.
There are few, if any, young
globular clusters in our
Milky Way Galaxy because
conditions are not ripe for more to form.
Things are different next door, however, in the neighboring
LMC galaxy.
Pictured above is a "young" globular cluster residing there:
NGC 1818.
Observations show it formed
only about 40 million years ago -
just yesterday compared to the 12 billion year ages of
globular clusters in our own
Milky Way
APOD: 2001 February 2 - All-Sky Panorama
Explanation:
This quite stunning panorama
of the entire sky is a mosaic of 51
wide-angle
photographs.
Made over a three year period from locations in
California (USA), South Africa, and Germany, the individual
pictures were
digitized and stitched together to create
an apparently seamless 360 by 180 degree view.
Using a mathematical prescription like one often
used to map
the whole Earth's surface onto a single flat image,
the complete digital mosaic was distorted and
projected onto an oval shape.
The image is oriented so the
plane of our Milky Way Galaxy
runs horizontally
through the middle with the
Galactic center at image center and
Galactic north at the top.
Most striking are the "milky"
bands of starlight from the
multitude of
stars in
the
galactic plane cut by the dark, obscuring dust clouds
strewn through the local spiral arms.
In fact, almost everything visible here is within our own
Milky Way Galaxy.
Two fuzzy patches in the lower right quadrant of the mosaic
do correspond to external galaxies, though.
Known as the
Magellanic
Clouds, these are small, nearby satellite
galaxies of the magnificent Milky Way.
APOD: 2001 January 28 - CMB Dipole: Speeding Through the Universe
Explanation:
Our
Earth is not at rest.
The Earth moves around the
Sun.
The Sun orbits the center of the
Milky Way Galaxy.
The Milky Way Galaxy orbits in the
Local Group of Galaxies.
The Local Group falls toward the
Virgo Cluster of Galaxies.
But these speeds are less than the speed that
all of these objects together move relative to the
cosmic microwave background (CMB).
In the
above all-sky map, radiation in the
Earth's direction of motion appears
blueshifted and hence hotter,
while radiation on the opposite side of the sky is
redshifted and colder.
The map indicates that the
Local Group moves at about 600 kilometers per
second relative to this
primordial radiation.
This high speed was initially unexpected and its
magnitude is still unexplained.
Why are we moving so fast?
What is out there?
APOD: 2000 November 30 - Palomar 13's Last Stand
Explanation:
Globular star cluster
Palomar 13
has roamed the halo of our
Milky Way Galaxy for the last 12 billion years.
The apparently sparse cluster of stars just left of center in
this composite color digital image,
it is one of the smallest, faintest
globular
clusters known.
(The bright foreground star near bottom
is unrelated and creates the spiky imaging artifacts.)
Observations spanning forty years indicate
that Palomar 13's
galactic halo orbit
is a highly eccentric one which, every one or two billion
years, brings it relatively close to the galactic center.
With each close approach to the
Milky Way's central regions,
gravitational tidal forces
strip away
the delicately bound cluster stars.
In fact, detailed present day studies offer evidence
for a dramatic end to this dwindling cluster's tidal
tug of war.
Palomar 13's latest close approach was only
about 70 million years ago.
But, when Palomar 13 again approaches the galaxy, it
could well turn out to be
the cluster's
last stand.
APOD: 2000 November 6 - Heaven on Earth
Explanation: If sometimes it appears that the entire
Milky Way Galaxy is raining down on your head,
do not despair.
It happens twice a day.
As the
Sun rises in the East,
wonders of the night sky become less bright than the
sunlight scattered by our own
Earth's atmosphere, and so fade from view.
They will only rotate back into view when the
Earth again eclipses our bright Sun at
dusk.
This battle between heaven and Earth was
captured dramatically above during the
last few minutes of daylight on 1999 August 10 in Koumi,
Japan.
Dark
dust, millions of
stars, and bright glowing
red gas highlight the
plane of our
Milky Way Galaxy,
which lies on average thousands of
light years behind
Earth's yellow and green reflecting
clouds.
APOD: 2000 September 8 - Andromeda Island Universe
Explanation:
How far can you see?
The most distant object easily visible to the unaided eye is
M31,
the great
Andromeda Galaxy
some two million light-years away.
Without a telescope, even this immense spiral galaxy appears
as an unremarkable, faint, nebulous cloud in the
constellation
Andromeda.
But a bright yellow nucleus, dark winding dustlanes, gorgeous blue
spiral arms and star clusters are recorded in this stunning
telescopic digital
mosaic of the nearby island universe.
While even casual
skygazers
are now inspired by the knowledge that there are
many distant galaxies like M31, astronomers
seriously debated
this fundamental concept only 80 years ago.
Were these "spiral nebulae" simply outlying components of our own
Milky Way Galaxy or were they instead "island universes" -- distant
systems of stars comparable to the Milky Way itself?
This question was central to the famous
Shapley-Curtis
debate
of 1920, which was later resolved by
observations of M31
in favor of Andromeda,
island
universe.
APOD: 2000 August 19 - ROSAT Explores The X-Ray Sky
Explanation:
Launched in 1990, the orbiting
ROSAT observatory explored the Universe by
viewing the entire
sky in x-rays -- photons with about
1,000 times more energy than visible light.
This
ROSAT survey produced the sharpest, most sensitive
image of the x-ray sky to date.
The all-sky image is shown with the plane of
our Milky Way Galaxy running
horizontally through the center.
Both x-ray brightness and relative energy
are represented with red, green, and blue colors indicating three
x-ray energy ranges (from lowest to highest).
Bright x-ray spots near the galactic plane are within our own Milky Way.
The brightest region (right of center) is toward the
Vela Pulsar and the Puppis
supernova remnant.
Bright sources beyond our Galaxy are also apparent, notably the
Virgo cluster
of galaxies (near top right) and
the
Large Magellanic Cloud (LMC).
The LMC is easy to find here as
several of the black stripes (blank areas caused by missing data) seem
to converge on its position (lower right).
Over large areas of the sky a general diffuse
background of x-rays dominates.
Hot gas in our own Galaxy provides
much of this background and gives rise to the grand
looping structures
visible in the direction of the galactic center (image center).
Unresolved extragalactic sources also add to this background, particularly
above and below the plane.
Despite the x-ray sky's exotic appearance,
a very familiar feature is visible -
the gas and dust clouds which line the plane of our galaxy
absorb x-rays as well
as optical light and produce the dark bands running
through the galactic center.
APOD: 2000 August 4 - M15: Dense Globular Star Cluster
Explanation:
Life might get dull
at the core of M15 but the
sky would always be
bright with stars!
In fact, only 40,000 light-years away in the constellation Pegasus, M15
is one of the most densely packed
globular star clusters
in our Milky Way Galaxy.
This stunning Hubble Space Telescope
image
of M15 shows
thousands of individual stars across the
central 10 or so light-years of the cluster,
also cataloged as NGC 7078.
Yet even the Hubble's sharp
vision
can't clearly separate the stars
at this cluster's
core.
Globular star clusters harbor
from a hundred thousand up to a million stars and roam
the
Milky Way halo.
Like most globulars,
M15 is filled with ancient stars, about 12 billion
years old compared to the Sun's estimated 4.5 billion years.
Its cool red giant stars appear yellowish in this color composite image.
Unlike most globulars, M15 displays
a planetary
nebula, the briefly
visible gaseous shroud of a dying star.
Can you pick it out?
Cataloged as Kuestner 648,
M15's planetary nebula is the
round pinkish cloud at the upper left.
APOD: 2000 June 29 - Galactic Centre Starscape
Explanation:
Thirty thousand light-years distant,
beyond the
majestic dust clouds of the constellation
Sagittarius, lies the centre of our Milky Way Galaxy.
Hidden from optical view by the dust, the
Galactic Centre region is
a relatively unexplored starscape.
But
infrared light can more easily
penetrate the dust and
this recently released
Infrared Space Observatory
(ISO)
mosaic, together with other similar images, shows about 100,000 previously
unseen stars of the Milky Way's central regions.
Huge obscuring dust clouds still seem to crowd the area
especially in the left part of the infrared picture.
Marked by the white circle, the centre itself is missing from the mosaic
because it is so bright that it would saturate ISO's sensitive camera.
The stars
are mostly evolved
red giants, intrinsically cool,
large, bright stars that have swollen after exhausting their central supply
of hydrogen fuel.
The detailed properties of the
red
giant stars can be
very revealing
as these stars contribute to the interstellar
gas and dust clouds, enriching their galactic environment with
carbon and
other elements.
Their motions also trace the mass distribution in the Galactic Centre and
may support the idea that our Galaxy grew by
swallowing smaller, nearby galaxies.
APOD: 2000 June 18 - The Milky Way Near the Southern Cross
Explanation:
This breathtaking patch of sky would be above you were you
to stand at the
South Pole of the Earth.
Just above and to the right of
this photograph's center
are the four stars that mark the
boundaries of the famous
Southern Cross.
At the top of this constellation, also known as
The Crux, is the orange star
Gamma Crucis.
The
band of stars, dust, and gas
crossing the middle of the photograph is part our
Milky Way Galaxy.
In the very center of the photograph is the dark
Coal Sack Nebula,
and the bright nebula on the far right is the
Carina Nebula.
The Southern Cross is such a famous constellation that it is
depicted on the
national flag of Australia.
APOD: 2000 February 22 - Neighboring Galaxy: The Large Magellanic Cloud
Explanation:
The brightest galaxy visible from our own Milky Way Galaxy is the
Large Magellanic Cloud (LMC).
Visible predominantly from
Earth's Southern Hemisphere, the
LMC is the second
closest galaxy,
neighbor to the
Small Magellanic Cloud,
and one of
eleven known dwarf galaxies that orbit our Milky Way Galaxy.
The
LMC is an
irregular galaxy composed of a bar of older red stars,
clouds of younger blue stars, and a bright red star forming
region visible near the top of the
above image called the
Tarantula Nebula.
The brightest
supernova of modern times,
SN1987A, occurred in the
LMC.
APOD: 2000 January 30 - The Milky Way in Infrared
Explanation:
At night, from a dark location, part of the clear sky looks
milky.
This unusual swath of dim light is generally visible during
any month and from any location.
Until the invention of the telescope,
nobody really knew what the "Milky Way" was.
About 300 years ago telescopes caused a startling revelation: the Milky Way was made of
stars.
Only 70 years ago,
more powerful telescopes
brought the further revelation that the
Milky Way is only one galaxy among many.
Now telescopes in space allow yet deeper understanding.
The
above picture was taken by the
COBE satellite
and shows the plane of our Galaxy in infrared light. The thin disk of our home
spiral galaxy
is clearly apparent, with stars appearing white and
interstellar dust appearing red.
APOD: 2000 January 21 - X For Andromeda
Explanation:
A big beautiful spiral galaxy 2 million light-years away,
Andromeda (M31)
has long been touted as an analog to the Milky Way,
a distant mirror of our own galaxy.
The popular 1960s British sci-fi series,
A For Andromeda,
even postulated that it was home to another technological civilization
that communicated
with us.
Using the newly unleashed observing power of the orbiting
Chandra X-ray telescope,
astronomers have now imaged the
center of our near-twin
island universe, finding evidence
for an object so bizarre it would have impressed many
60s science fiction writers (and readers).
Like the Milky Way,
Andromeda's galactic center appears to
harbor an X-ray source characteristic of
a black hole of a million or more solar masses.
Seen above,
the false-color X-ray picture shows a number of
X-ray sources, likely
X-ray binary stars, within
Andromeda's central region as yellowish dots.
The blue source located right at the galaxy's center is coincident
with the position of the suspected massive black hole.
While
the X-rays are produced as material falls into the
black hole and heats up, estimates from the X-ray data show Andromeda's
central source to be surprisingly cool - only a million
degrees or so compared to the tens of millions of degrees
indicated for Andromeda's X-ray binaries.
APOD: 2000 January 20 - X-Rays From The Galactic Center
Explanation:
Exploring quasars
and active galaxies in the distant
universe, astronomers have come to believe that
most galaxies have massive black holes at their centers.
Swirling stars and a strong, variable
radio source offer convincing evidence that even our own Milky Way
galaxy's center harbors such a
bizarre object,
a mere 30,000 light-years away.
Still, it has long been realized that if a massive black hole
lurks there
it should produce X-rays
- which have not previously been identified.
Now, though relatively faint,
the missing X-ray source may have been found.
Taking advantage of the sensitive Chandra Observatory
astronomers have recorded this false-color
X-ray image of the Galactic Center.
Embedded in a diffuse cloud of
X-ray hot gas,
the white dot at the center corresponds to an X-ray
source at exactly the position of the strong radio source
and suspected black hole.
Other individual X-ray sources are also present in
the picture which spans about 10 light-years at the distance
of the galactic center.
With radio and X-ray emission generated by infalling material,
the Milky Way's central black hole is thought to have a mass of
over 2 million suns.
APOD: December 30, 1999 - The Century that Defined Galaxy
Explanation:
As the
twentieth century dawned a
debate raged over whether the
Milky Way
was the entire universe.
The 1920s brought
observations of
spiral-nebulae
that housed familiar but faint
variable stars,
and hence placed these
nebulae much farther
than anything else ever found.
The Milky Way, apparently, is itself a
spiral nebula seen from the inside.
Soon interstellar dust was
identified as the opaque material that blocks our view of distant
spiral arms, confirming that our
Sun was well away from the center.
As the twentieth century closes, galaxies are seen
forming across the universe,
and our Milky Way is referred to as a spiral galaxy quite similar to
NGC 1288, as
pictured above.
APOD: December 18, 1999 - Irregular Galaxy Sextans A
Explanation:
Grand spiral galaxies
often seem to get all the glory.
Their newly formed, bright, blue
star clusters
found along beautiful, symmetric
spiral arms
are guaranteed to attract attention.
But
small irregular galaxies
form stars too,
like this lovely, gumdrop-shaped galaxy,
Sextans A.
A member of
the local group of galaxies which includes the massive
spirals Andromeda and our own
Milky Way,
Sextans A is about
10 million light years distant.
The bright Milky Way foreground stars appear yellowish
in this view. Beyond them lie the stars of
Sextans A with tantalizing
young blue clusters clearly visible.
APOD: December 14, 1999 - High Velocity Clouds and the Milky Way
Explanation:
Where are these gas clouds going so quickly?
High velocity clouds (HVCs) of gas
have been seen for decades but their origins and
destinations have remained mysterious.
Recent measurements have now placed at least
one of these clouds in the halo of our
Milky Way Galaxy, while other measurements
have determined the relative abundance of cloud elements.
Of the two clouds measured, each appears to have a
chemical abundance consistent with a different origin.
One HVC has been measured to have very few heavy elements
("low metallically") compared to neighboring stars,
while another HVC has been inferred to have a
heavy element abundance more typical of neighboring stars.
Hypotheses are therefore being investigated that
some HVCs are local gas remnants being
pushed away from our Galaxy by
supernova explosions, while other
HVCs are ancient
dwarf galaxy
remnants falling toward our Galaxy.
The latter possibility is particularly
interesting as it might help explain how our
Galaxy can continue to
make stars at the observed rate.
Fast moving HVCs are circled in the above false-color mosaic.
APOD: October 9, 1999 - The Frothy Milky Way
Explanation:
Astronomers have discovered that looking at dust along
the plane of our Milky Way Galaxy
is a bit like looking into a frothy glass of beer.
The dust between stars
in our galaxy appears to be arranged
like a foam with bubbles and voids -- churned by
shocks and winds generated
as stars cycle through their lives.
This processed
infrared image, based on
data from NASA's IRAS satellite, maps the radiation from
the edges of galactic dust clouds and reveals the complex distribution.
The image covers an area of about 40x60
degrees centered on the
galactic plane near the Cygnus region.
It shows bright bubble-shaped
and arc-like dust clouds around the
supernova remnants and
starbirth regions embedded in the galactic disk.
APOD: October 3, 1999 - Nearby Dwarf Galaxy Leo I
Explanation:
Leo I is a
dwarf spheroidal galaxy in the
Local Group of galaxies dominated by our
Milky Way Galaxy and
M31.
Leo I is thought to be the most distant of
the eleven known small satellite galaxies orbiting our
Milky Way Galaxy.
Besides the
LMC and the
SMC,
all Milky Way satellite galaxies are
small,
dim, dwarf spheroidals, including the closest galaxy - the
Sagittarius
Dwarf.
Leo I is more distant than most of them,
thought to be about 250 kpc away.
Although very little star-forming gas is visible in
Leo I, analysis of
star ages shows that stars have
formed as recently as a billion years ago.
APOD: September 27, 1999 - Our Galaxy in Stars, Gas, and Dust
Explanation:
The disk of our
Milky Way Galaxy is home to hot nebulae,
cold dust, and billions of stars.
The red nebulae visible in the above contrast-enhanced picture are primarily
emission nebulae,
glowing clouds of hydrogen gas heated by nearby, bright, young stars.
The blue nebulae are primarily
reflection nebulae,
clouds of gas and fine dust reflecting the light of nearby bright stars.
Perhaps the most striking, though, are the areas of darkness,
including the Pipe Nebula
visible on the image top left.
These are lanes of thick dust,
many times containing relatively cold
molecular clouds of gas.
Dust is so plentiful that it obscures the
Galactic Center in visible light,
hiding its true direction until discovered
early this century.
The diffuse glow comes from
billions of older,
fainter stars like our
Sun, which are typically much older than any of the nebulae.
Most of the mass of our Galaxy remains in a form currently unknown.
APOD: June 27, 1999 - COBE Dipole: Speeding Through the Universe
Explanation:
Our Earth is
not at rest. The Earth moves around the
Sun.
The Sun orbits the center of the
Milky Way Galaxy.
The Milky Way Galaxy orbits in the
Local Group. The Local Group falls toward the
Virgo Cluster of Galaxies.
But these speeds are less than the speed that all of these objects
together move relative to the
microwave background.
In the above all-sky map,
radiation in the Earth's direction of motion appears blueshifted
and hence hotter, while radiation on the opposite side of the
sky is redshifted and colder.
The map indicates that the Local Group moves at about 600 kilometers per
second relative to this primordial radiation.
This high speed was initially unexpected and its
magnitude is still unexplained. Why are we moving so fast?
What is out there?
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 26, 1999 - USNO A2.0 Catalog: A Digital Sky
Explanation:
Here lie 526,230,881 of the brightest stars known.
The US Naval Observatory has deployed their monster
Precision Measuring Machine to digitize
photographic plates covering the whole sky and creating the
above map.
Yellow corresponds to 150,000 stars per square degree,
while dark blue corresponds to only 500 stars per square degree.
(For comparison, the
Full Moon
takes up about 1/4 of a square degree.)
The most striking feature on this
whole sky projection is the
central disk of our
Milky Way Galaxy, which stretches across the middle.
Dark
dust
lanes are evident there by the
great number of stars they obscure.
The two bright spots seen south of the
Milky Way's disk are the neighboring
Magellanic Cloud galaxies.
Anyone can
order a free copy of this data,
but not everyone can fit data from all
526,230,881 stars on their hard-drive.
APOD: April 10, 1999 - Canaries Sky
Explanation:
This gorgeous view of stars, nebulae, and the Milky Way
comes from
the dark night sky above
the lovely island of
La Palma in the Canaries archipelago.
The picture was made by a group of experienced astrophotographers
who traveled there to take advantage of the ideal
observing conditions near La Palma's
Observatorio del Roque de los Muchachos.
Skygazers can easily pick out several of their
favorite astronomical objects
in this wide angle time exposure which
covers about 40 degrees on winter the
sky.
Faint stars along the plane of our Galaxy compose the delicate,
luminous band of the Milky Way
stretching across the image from the bottom left.
The familiar constellation
of Orion the hunter is also easy to find,
with glowing nebulae
highlighting the hunter's belt and sword.
Orion's
famous red giant star
Betelgeuse, near picture center,
has a yellowish cast and
Rigel is the bright star in
Orion at lower right.
Brilliant white
Sirius, near the bottom, is the brightest
star in the picture (and in Earth's night sky).
Sirius, is part of
the constellation Canis Major (Big Dog).
Across the Milky Way, above and to the left of Sirius, is slightly
less brilliant Procyon, brightest star of
Canis Minor.
A V-shaped group of yellowish stars at the upper right, part of
Taurus the bull,
is dominated by the red giant
Aldebaran.
APOD: February 26, 1999 - Dark Cloud
Explanation:
Ominously foreshadowing events to come,
a dark cloud of obscuring dust stands
out against a luminous star field in
the Milky Way.
Cataloged as
Feitzinger and Stuwe object "1-457" this
fuliginous
interstellar nebula is relatively close -
possibly only 1,000 light-years distant.
Near its core it is dense enough to
block almost all of the light from the numerous,
more distant stars visible toward
the galactic center region.
In addition to
dust grains,
dark nebulae which abound in the plane of our
Galaxy are likely to contain
interstellar gas and represent
potential raw material for future star formation.
APOD: February 25, 1999 - NGC 6712: Galactic Globular Cluster
Explanation:
Following orbits which loop
high above the galactic plane,
globular star clusters are probably 12 to 14 billion years old -
truly ancient denizens of our Milky Way Galaxy.
After analyzing these new ESO/VLT
images of portions of the globular cluster NGC 6712,
astronomers report that this dense grouping of about 1 million stars
seems to be slowly dissolving - steadily loosing fainter, lower mass
stars into our Galaxy's halo.
Their results offer strong evidence for
gravitational stripping of stars from clusters which pass through
the plane and central regions of the Galaxy.
One of
about 150 globular clusters known to be members of the Milky Way,
NGC 6712 is thought to have
crossed through the crowded galactic plane
only a few million years ago.
NGC 6712 is about 23,000 light-years away in the
southern constellation Scutum.
APOD: February 24, 1999 - A Milky Way Band
Explanation:
Most bright stars in our
Milky Way Galaxy reside in a disk.
Since our Sun also resides in this disk, these stars
appear to us as a
diffuse band that circles the sky.
The above panorama of a
southern band of the
Milky Way's disk was taken from
Australia.
A 40-minute exposure was used, and the colors were digitally enhanced.
Visible are many
bright stars,
dark dust lanes,
red emission nebulae,
blue reflection nebulae, and
clusters of stars.
In addition to all this matter that we can see,
astronomers suspect there exists even more
dark matter that we cannot see.
APOD: February 3, 1999 - A Galactic Mushroom Cloud
Explanation:
Part of our Galaxy is exploding.
Recent radio observations show new details
of hot gas expanding rapidly from an energetic
star-forming region in our
Galactic disk out into our
Galaxy's halo.
The combined power of at least hundreds of
supernovae
is needed to drive this tremendous expansion.
The resulting 1000 light-year
mushroom cloud dwarfs any Earth-borne nuclear explosion, but is small
compared to the 60,000 light-year diameter of our
Milky Way's disk.
The mushroom cloud is one of
many similar plumes, and provides
important clues to the origin and nature of the Milky Way's
mysterious hot gas halo.
APOD: January 28, 1999 - The Galactic Center A Radio Mystery
Explanation:
Tuning in to the center of our Milky Way galaxy, radio astronomers
explore a complex, mysterious place.
A premier high resolution view,
this startlingly beautiful picture
covers a 4x4 degree region around the galactic center.
It was constructed from 1 meter wavelength radio data
obtained by telescopes of the
Very Large Array near
Socorro, New Mexico, USA.
The galactic center
itself is at the edge of the extremely
bright object labeled Sagittarius (Sgr) A, suspected of harboring
a million solar mass black hole.
Along the galactic plane which runs diagonally
through the image are tortured clouds of gas energized by
hot stars and round-shaped supernova remnants (SNRs)
- hallmarks of
a violent and
energetic cosmic environment.
But perhaps most intriguing are
the arcs, threads, and filaments which
abound in the scene.
Their uncertain origins challenge
present theories of the dynamics of the galactic center.
APOD: January 17, 1999 - NGC 1818: A Young Globular Cluster
Explanation:
Globular clusters
once ruled the Milky Way. Back in
the old days, back when our Galaxy
first formed, perhaps thousands of globular clusters roamed our
Galaxy.
Today, there are perhaps 200 left. Many globular clusters were destroyed
over the eons by repeated fateful encounters with each other or
the Galactic center.
Surviving relics are older than any earth fossil,
older than any other structures in our Galaxy, and limit the universe itself in raw age.
There are few, if any, young globular clusters
in our Milky Way Galaxy because conditions
are not ripe for more to form. But things are different next
door - in the neighboring LMC galaxy.
Pictured above is a "young" globular cluster residing
there: NGC 1818.
Recent observations show it formed only about 40 million years
ago - just yesterday compared to the 12 billion year ages
of globular clusters
in our own Milky Way
APOD: November 26, 1998 - Meteor Milky Way
Explanation:
The bold, bright
star patterns of Orion (right) are a
familiar sight to even casual skygazers.
But this gorgeous color photo also features a subtler
spectacle - the faint stars
of the Milky Way.
A broad region of
the Milky Way
runs vertically through the picture
with the striking
red Rosette Nebula in bloom left of center.
Cutting across this dim, diffuse band of stars which lie along
the plane of our Galaxy is a meteor streak.
It seems to pass just under
the red-orange giant star Betelgeuse at
Orion's shoulder.
Astrophotographer
Jeff Medkeff recorded
this and other beautiful time exposures from
a dark sky countryside southeast of Sierra Vista, Arizona USA,
during
November's Leonid
meteor shower.
APOD: August 26, 1998 - The Magellanic Stream
Explanation:
Spanning the sky behind the majestic
Clouds of Magellan
is an unusual stream of gas: the Magellanic Stream.
The origin of this gas might hold a clue to
origin and fate of our
Milky Way's
most famous satellite galaxies: the
LMC and the
SMC.
Two leading genesis hypotheses have surfaced:
that the stream was created by gas stripped off these galaxies as
they passed through the halo of our Milky Way,
or that the stream was created by the differential gravitational tug of the Milky Way.
Measurements of slight angular motions by the
Hipparcos satellite have indicated that the
Clouds are leading the Stream.
Now, recent radio measurements have located
fresh gas emerging from the Clouds,
bolstering the later, tidal explanation.
Most probably, in a few hundred million years, the
Magellanic Clouds themselves will fall victim
to this same tidal force.
APOD: August 17, 1998 - Comet Hyakutake and the Milky Way
Explanation:
Two years ago, the
Great Comet of 1996,
Comet Hyakutake,
inched across our northern sky during its
long orbit around the
Sun. Visible above as the
bright spot with the
faint tail
near the picture's center,
Comet Hyakutake
shares the stage with part of the central band of the
Milky Way Galaxy,
prominent in the picture's upper right. Also visible are
Antares,
the bright orange star in the upper right, Arcturus, the bright star on the lower left, and the
Pipe Nebula,
which is perhaps harder to find.
Comet Hyakutake's
unusually close approach to the
Earth allowed astronomers
to learn many things, including that
comets can emit much X-ray light.
APOD: July 29, 1998 - The High Energy Heart Of The Milky Way
Explanation:
These high resolution false color pictures of the Galactic center
region in high energy
X-ray and gamma-ray light result from a very long
exposure of roughly 3,000 hours performed from 1990 to 1997 by the
French SIGMA telescope onboard the
Russian GRANAT spacecraft.
Each image covers a 14x14 degree field which includes most of the
central bulge of
our Milky Way Galaxy.
The X-ray picture (left) reveals a cluster of sources
releasing enormous amounts of energy.
They are probably
binary star systems where matter accretes
onto a collapsed object, either
a neutron star or
a black hole.
But
according to recent theories, only those
binary systems with black holes
can radiate above X-ray energies -- in the gamma-ray regime.
In that case, the SIGMA sources also shining in the gamma-ray picture
(right) betray the presence of accreting
stellar black holes!
Surprisingly, no high energy source seems to coincide exactly
with the Galactic center itself,
located near the brightest source at the bottom of both
pictures.
This indicates that
the large black hole
thought
to be lurking there
is unexpectedly quiet at these energies.
APOD: May 23, 1998 - 7,000 Stars And The Milky Way
Explanation:
This panorama
view of the sky
is really a drawing.
It was made in the 1950s under the supervision
of astronomer Knut Lundmark at the
Lund Observatory in Sweden.
To create the picture, draftsmen used
a mathematical distortion to map
the entire sky onto an oval shaped image with
the plane of our Milky Way Galaxy
along the center and the north galactic
pole at the top.
7,000 individual stars are shown as white dots, size
indicating brightness.
The "Milky Way" clouds, actually the combined
light of dim, unresolved stars in the
densely populated galactic plane, are
accurately painted on, interrupted by
dramatic dark dust lanes.
The overall effect is photographic in quality and represents the visible
sky.
Can you identify any familiar
landmarks or constellations?
For starters,
Orion
is at the right edge of the picture, just below the galactic plane
and the Large and
Small Magellanic Clouds are visible as
fuzzy patches in the lower right quadrant.
APOD: May 2, 1998 - The Frothy Milky Way
Explanation:
Astronomers have discovered that looking at dust along
the plane of our Milky Way Galaxy
is a bit like looking into a frothy glass of beer.
The dust between stars
in our galaxy appears to be arranged
like a foam with bubbles and voids -- churned by
shocks and winds generated
as stars cycle through their lives.
This processed
infrared image, based on
data from NASA's IRAS satellite, maps the radiation from
the edges of galactic dust clouds and reveals the complex distribution.
The image covers an area of about 40x60 degrees centered on the
galactic plane near the Cygnus region.
It shows bright bubble-shaped
and arc-like dust clouds around the
supernova remnants and
starbirth regions embedded in the galactic disk.
APOD: March 7, 1998 - NGC 1818: A Young Globular Cluster
Explanation:
Globular clusters
once ruled the Milky Way. Back in
the old days, back when our Galaxy
first formed, perhaps thousands of globular clusters roamed our
Galaxy. Today, there are perhaps 200 left.
Many globular clusters were destroyed
over the eons by repeated fateful encounters with each other or
the Galactic center. Surviving relics
are older than any earth fossil,
older than any other structures in our Galaxy,
and limit the universe itself
in raw age. There are few, if any, young globular clusters
in our Milky Way Galaxy because conditions
are not ripe for more to form. But things are different next
door - in the neighboring LMC galaxy.
Pictured above is a "young" globular cluster residing
there: NGC 1818.
Recent observations show it formed only about 40 million years
ago - just yesterday compared to the 12 billion year ages
of globular clusters
in our own Milky Way
APOD: March 5, 1998 - Canaries Sky
Explanation:
This gorgeous view of stars, nebulae, and the Milky Way
comes from
the dark night sky above
the lovely island of
La Palma in the Canaries archipelago.
The picture was made by a group of experienced astrophotographers
who traveled there to take advantage of the ideal
observing conditions near La Palma's
Observatorio del Roque de los Muchachos.
Skygazers can easily pick out several of their
favorite astronomical objects
in this wide angle time exposure which
covers about 40 degrees on winter the
sky.
Faint stars along the plane of our Galaxy compose the delicate,
luminous band of the Milky Way
stretching across the image from the bottom left.
The familiar constellation
of Orion the hunter is also easy to find,
with glowing nebulae
highlighting the hunter's belt and sword.
Orion's
famous red giant star
Betelgeuse, near picture center,
has a yellowish cast and
Rigel is the bright star in
Orion at lower right.
Brilliant white
Sirius, near the bottom, is the brightest
star in the picture (and in Earth's night sky).
Sirius, is part of
the constellation Canis Major (Big Dog).
Across the Milky Way, above and to the left of Sirius, is slightly
less brilliant Procyon, brightest star of
Canis Minor.
A V-shaped group of yellowish stars at the upper right, part of
Taurus the bull,
is dominated by the red giant
Aldebaran.
APOD: February 26, 1998 - A Southern Sky View
Explanation:
From horizon to horizon,
the night sky above Loomberah, New South Wales, Australia
was photographed by astronomer
Gordon Garradd
on March 22, 1996.
Garradd used a home made all-sky camera with a
fish-eye lens,
resulting in a circular 200 degree field of view.
This gorgeous sky view is dominated by the luminous band of
the Milky Way
cut by dramatic, dark interstellar dust clouds.
Along with the bright stars of our Galaxy,
the Large Magellanic Cloud
is visible at the upper right (about 1 o'clock)
and the
long, lovely, bluish tail of
comet Hyakutake can be seen
toward the bottom of the image, near the bright star
Arcturus.
Bright city lights from nearby Tamworth glow along
the Northwestern horizon.
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: February 16, 1998 - Sagittarius Dwarf to Collide with Milky Way
Explanation:
Our Galaxy is being invaded. Recent observations indicate that in
the next 100 million years, the
Sagittarius Dwarf galaxy
will move though the disk of our own
Milky Way Galaxy
yet again . The
Sagittarius Dwarf (Sgr), shown as the extended irregular
shape below the Galactic Center,
is the closest of 9 known small
dwarf spheroidal galaxies that orbit our Galaxy.
Don't worry, our Galaxy is not in danger,
but no such assurances are issued for the
Sagittarius Dwarf: the intense gravitational
tidal forces might pull it apart. Oddly, however,
Sgr's orbit indicates that is has been through
our Galaxy several times before, and survived!
One possibility is that Sgr contains a great deal of
low-density dark matter that hold it together
gravitationally during these collisions.
APOD: January 24, 1998 - The Large Cloud Of Magellan (LMC)
Explanation:
Ferdinand Magellan and his
crew had plenty of time to study
the southern sky during their
famous voyage around the world.
As a result, two fuzzy cloud-like
objects, not visible to
northern hemisphere dwellers,
are now known as the Clouds of Magellan.
These star clouds are small irregular galaxies,
satellites of our larger Milky Way spiral galaxy.
The Large Magellanic Cloud (LMC)
pictured above is only about 180,000 light-years distant - the
only known galaxy closer is the
Sagittarius Dwarf.
Both the LMC and the Small Magellanic Cloud (SMC)
are joined to the
Milky Way by a
stream of cold hydrogen gas.
An unusual effect called gravitational lensing
has recently been detected in a few LMC stars,
and there is hope this could tell us important information about
the true composition of our universe.
APOD: December 29, 1997 - The Milky Way in Infrared
Explanation:
At night, from a dark location, part of the clear sky looks
milky.
This unusual swath of dim light is generally visible during
any month and from any location.
Until the invention of the telescope,
nobody really knew what the "Milky Way" was.
About 300 years ago telescopes caused a startling revelation: the Milky Way was made of
stars.
Only 70 years ago,
more powerful telescopes
brought the further revelation that the
Milky Way is only one galaxy among many.
Now telescopes in space allow yet deeper understanding.
The
above picture was taken by the
COBE satellite
and shows the plane of our Galaxy in infrared light. The thin disk of our home
spiral galaxy
is clearly apparent, with stars appearing white and
interstellar dust appearing red.
APOD: November 14, 1997 - Irregular Galaxy Sextans A
Explanation:
Grand spiral
galaxies often seem to get all the glory.
Their newly formed, bright, blue
star clusters
found along beautiful, symmetric
spiral arms
are guaranteed to attract attention.
But small
irregular galaxies form stars too,
like this lovely, gumdrop-shaped galaxy,
Sextans A.
A member of
the local group of galaxies which includes the massive
spirals Andromeda and our own
Milky Way,
Sextans A is about
10 million light years distant.
The bright Milky Way foreground stars appear yellowish
in this view. Beyond them lie the stars of
Sextans A with tantalizing
young blue clusters clearly visible.
APOD: November 5, 1997 - The Milky Way's Gamma-Ray Halo
Explanation:
Our Milky Way galaxy appears to be surrounded by a halo of gamma rays.
Gamma rays are the most energetic form of
electromagnetic radiation, with
more than a hundred thousand times the energy of visible light,
but known gamma-ray sources
don't account for the diffuse distribution of this high-energy glow.
This surprising result
is based on data
from the EGRET instrument onboard
the Compton Gamma Ray Observatory.
In this false color
all-sky image centered on
the Milky Way, the
brown and green regions indicate brighter, known sources of gamma-rays.
The galactic center and plane clearly standout as do some
distant galaxies seen near the top and bottom of the picture.
The dim, blue regions above and
below the plane correspond to our Galaxy's unexpected gamma-ray halo.
What causes the halo?
Future gamma-ray telescopes
could solve this mystery.
However, the excitement has already inspired tantalizing
speculation about the solution including;
collisions of low energy photons with
high-energy cosmic rays,
high energy electrons accelerated by a previous burst of
Milky Way star formation,
and exotic interacting particles which make up
Dark Matter.
APOD: October 3, 1997 - Comet Halley and the Milky Way
Explanation:
Comet Halley was photographed superposed in front of the disk of our
Milky Way Galaxy in 1986 by the
Kuiper
Airborne Observatory. Comet Halley is the bright white streak near this photograph's center.
Comet Halley is the most
famous comet in history, and returns to the inner
Solar System every 76 years.
Stars visible in our
Milky Way Galaxy typically lie
millions of times farther in the distance and
orbit the
Galactic center every 250 million years.
Billions of
comets are thought to orbit our
Sun
but most do not get close enough for us to see.
Similarly, billions of stars orbit our Milky Way's center but do not get close enough for us to see.
APOD: July 19, 1997 - The Small Cloud of Magellan
Explanation:
The southern sky contains wonders almost unknown in the north.
These wonders include the
Large and Small
Magellanic
Clouds: small irregular
galaxies orbiting our own larger
Milky Way spiral galaxy. The
Small
Magellanic Cloud (SMC), pictured here, is about 250,000 light years away.
The SMC contains many young, hot, blue stars indicating it has
undergone a recent period of star formation,
possibly due to a collision with the LMC 500 million years ago.
The bright object on the right is a
globular cluster near the outskirts of the
Milky Way.
APOD: May 17, 1997 - 7,000 Stars and the Milky Way
Explanation:
This panorama
view of the sky is really a drawing.
It was made in the 1940s under the supervision of astronomer Knut Lundmark at
the Lund Observatory
in Sweden. To create the picture, draftsmen used
a mathematical distortion to map
the entire sky onto an oval shaped image with
the plane of our Milky Way Galaxy
along the center and the north galactic
pole at the top. 7,000 individual stars are shown as white dots, size
indicating brightness. The "Milky Way" clouds, actually the combined
light of dim, unresolved stars in the
densely populated galactic plane, are
accurately painted on, interrupted by
dramatic dark dust lanes.
The overall effect is photographic in quality and represents the visible
sky. Can you identify any familiar landmarks or constellations?
For starters,
Orion
is at the right edge of the picture, just below the galactic plane
and the Large and
Small Magellanic Clouds are visible as
fuzzy patches in the lower right quadrant.
APOD: April 30, 1997 - Milky Way Molecule Map
Explanation:
Where are the Milky Way's gas clouds and where are they going?
Stars form in gas clouds,
and the motion of gas clouds tell us about the
size and rotation speed of our own
Milky Way Galaxy.
But gas clouds are hard to detect - they are
composed mostly of nearly invisible molecular
hydrogen and
helium.
Fortunately, at least small amounts of heavier gases co-exist, one of them being
carbon monoxide (CO),
which is relatively easy to detect at radio wavelengths.
Therefore, over the past decade, a
team of astronomers have
carefully
mapped out the molecular sky to unprecedented
clarity - to about four times previous resolution
and about eight times previous sensitivity. The resulting
map is shown above,
rescaled and in false color, with dark blue
being relatively low emission. The band of our
Milky Way Galaxy
spans the middle. The data have not only helped our understanding of the
Galaxy,
but highlight a few mysteries too. For example:
what
causes the rapid speed of the gas near the
Galactic Center?
APOD: April 24, 1997 - The Frothy Milky Way
Explanation:
Astronomers have recently discovered that looking at dust along
the plane of our Milky Way Galaxy
is a bit like looking into a frothy glass of beer.
The dust between stars
in our galaxy is arranged
like a foam with bubbles and voids -- apparently churned by
shocks and winds generated
as stars cycle through their lives.
This processed
infrared image, based on
data from NASA's IRAS satellite, maps the radiation from
the edges of galactic dust clouds and reveals the complex distribution.
The image covers an area of about 40x60 degrees centered on the
galactic plane near the Cygnus region.
It shows bright bubble-shaped
and arc-like dust clouds around the
supernova remnants and
starbirth regions embedded in the galactic disk.
APOD: April 23, 1997 - Antlia: A New Galactic Neighbor
Explanation: Meet Antlia, a newly discovered neighbor of
our Milky Way Galaxy. Announced just last week, this faint member
of our Local Group of Galaxies
has only about one million stars. It is late in being noticed
because it is so hard to see against a bright sky.
This faint galaxy is seen here in the background - the bright stars
visible are in our own galaxy.
The Antlia Dwarf Galaxy
is actually a dwarf spheroidal galaxy,
similar to nine known dwarf spheroidals that orbit our Milky Way
Galaxy. Antlia,
named for the constellation
in which it resides, is unusual because it does not hover near
either of the two major galaxies of the Local Group: our Milky Way Galaxy
and M31.
APOD: March 29, 1997 - The Closest Galaxy: The Sagittarius Dwarf
Explanation: What's the closest galaxy to our Milky Way?
For many years astronomers thought it was the Large Magellanic Cloud
(LMC). But the seemingly insignificant fuzzy patch shown above
turned out to be part of a galaxy that is even closer. Deemed
the "Sagittarius Dwarf",
this small galaxy went unnoticed until its discovery in 1994 by
R. Ibata, G. Gilmore and M. Irwin (RGO).
The reason the Sagittarius Dwarf hadn't been discovered earlier
is because it is so dim, it is so spread out over the sky, and
there are so many Milky Way stars in front of it. The distance
to the Sagittarius Dwarf
was recently measured to be about one third of the distance to
the LMC. Astronomers now believe that this galaxy is slowly being torn apart
by the vast gravitational forces of our Galaxy.
APOD: March 15, 1997 - The Milky Way's Center
Explanation: Although the Earth is round, our Galaxy appears
truly flat. This was shown in dramatic fashion by the COsmic Background Explorer (COBE)
satellite which produced this premier view of the central region
of our own Milky Way Galaxy
in infrared light in1990. The Milky Way
is a typical spiral galaxy with a
central bulge and extended disk of stars. However, gas and dust
within the disk obscure visible wavelengths of light effectively
preventing clear observations of the center. Since infrared
wavelengths are less affected by the obscuring material, the Diffuse InfraRed Background Experiment (DIRBE)
on board COBE
was able to detected infrared light from stars surrounding the Galactic center
and produce this image. Of course, the edge on perspective represents
the view from the vicinity of our Sun,
a star located in the disk about 30,000 light years out from the
center. The DIRBE
module used equipment cooled by a tub of liquid helium to detect
the infrared light which, composed of wavelengths longer than red light,
is invisible to the human eye.
APOD: March 8, 1997 - COBE Dipole: Speeding Through the Universe
Explanation: Our Earth is
not at rest. The Earth moves around the Sun.
The Sun orbits the center of the Milky Way Galaxy.
The Milky Way Galaxy orbits in the Local Group.
The Local Group falls toward the Virgo Cluster of Galaxies.
But these speeds are less than the speed that all of these objects
together move relative to the microwave background.
In the above all-sky map,
radiation in the Earth's direction of motion appears blueshifted
and hence hotter, while radiation on the opposite side of the
sky is redshifted and colder. The map indicates that the Local Group
moves at about 600 kilometers per second relative to this primordial radiation.
This high speed was initially unexpected and its magnitude is
still unexplained. Why are we moving so fast? What is out there?
APOD: March 4, 1997 - Solar Wind And Milky Way
Explanation:
The Sun is bright,
so bright that it overwhelms the light
from other stars even for most satellite-borne telescopes.
But LASCO, a coronograph onboard the
space-based SOHO Observatory, uses
occulting disks to block the intense solar light and examine
the tenuous, hot gases millions of miles above the Sun's surface.
In this
LASCO image from
December 24, 1996,
an occulting disk (center) and mechanical
support (extending from the lower left) are visible along with
the billowing Solar Wind.
Appearing in the background are
faint stars and obscuring dust clouds toward
the center of our Milky Way Galaxy!
The field of view covers about 16 degrees, corresponding to
28 million miles at the distance of the Sun - just under half the diameter
of Mercury's orbit.
A prominent dark interstellar dust cloud cuts through
the Milky Way starfield
running approximately south (lower right) to north.
Blemishes on the image are camera streaks caused by charged particles.
APOD: February 14, 1997 - NGC 1818: A Young Globular Cluster
Explanation: Globular clusters
once ruled the Milky Way. Back in
the old days, back when our Galaxy
first formed, perhaps thousands of globular clusters roamed our
Galaxy. Today, there are perhaps 200 left.
Many globular clusters were destroyed
over the eons by repeated fateful encounters with each other or
the Galactic center. Surviving relics
are older than any earth fossil,
older than any other structures in our Galaxy,
and limit the universe itself
in raw age. There are few, if any, young globular clusters
in our Milky Way Galaxy because conditions
are not ripe for more to form. But things are different next
door - in the neighboring LMC galaxy.
Pictured above is a "young" globular cluster residing
there: NGC 1818.
Recent observations show it formed only about 40 million years
ago - just yesterday compared to the 12 billion year ages
of globular clusters
in our own Milky Way
APOD: December 12, 1996 - The Milky Way Through the Summer Triangle
Explanation: There are more than a few stars in our Galaxy.
The light from many of them combines to appear as a wisp of faint
light across the night sky - the Milky Way.
In the northern hemisphere, away from city lights
and during the summer months, part of the Milky Way
can be seen behind the Summer Triangle
of stars - Deneb,
Vega,
and Altair.
These are the brightest three stars in the above photograph,
listed from left to right, respectively. If you could collect
light in your eyes for 10 minutes at a time (instead of the usual
1/10th of a second), you might see something like the
above photograph.
Behind the Summer Triangle
lies some of the vast star fields
of our Milky Way Galaxy, containing
literally billions
of stars. The dark band across the middle that seems to divide
the stars is actually interstellar dust,
which absorbs more visible light than it emits and so appears
dark.
APOD: October 23, 1996 - The Large Cloud of Magellan (LMC)
Explanation: Magellan and his
crew had plenty of time to study the southern sky during their
famous voyage around the world. As a result, two fuzzy cloud like
objects in the southern sky are now known as the Clouds of Magellan.
These star clouds are small irregular galaxies,
satellites of our larger Milky Way spiral galaxy.
The Large Magellanic Cloud (LMC)
pictured above is only about 180,000 light-years distant - the
only known galaxy closer is the Sagittarius Dwarf.
Both the LMC and the Small Magellanic Clouds (SMC)
are joined to the Milky Way by a
stream of cold hydrogen gas whose origin
is still controversial. An unusual effect called gravitational lensing
has recently been detected in a few LMC stars,
and there is hope this could tell us important information about
the true composition of our universe.
APOD: October 8, 1996 - ROSAT Explores The X-Ray Sky
Explanation:
Launched in 1990, the orbiting
ROSAT observatory explored the Universe by
viewing the entire
sky in x-rays - photons with about 1,000 times
more energy than visible light.
This ROSAT survey produced the sharpest, most sensitive
image of the x-ray sky to date.
The all-sky image is shown with
the plane of our Milky Way Galaxy running
horizontally through the center. Both x-ray brightness and relative energy
are represented with red, green, and blue colors indicating three
x-ray energy ranges (from lowest to highest).
Bright x-ray spots near the galactic plane are within our own Milky Way.
The brightest region (right of center) is toward the Vela Pulsar and the
Puppis supernova remnant.
Bright sources beyond our Galaxy are also
apparent, notably the Virgo cluster of galaxies
(near top right) and
the Large Magellanic Cloud (LMC).
The LMC is easy to find here as
several of the black stripes (blank areas caused by missing data) seem
to converge on its position (lower right).
Over large areas of the sky a general diffuse background of
x-rays dominates. Hot gas in our own Galaxy provides
much of this background and gives rise to the grand looping structures
visible in the direction of the galactic center (image center).
Unresolved extragalactic sources also add to this background, particularly
above and below the plane.
Despite the x-ray sky's exotic appearance,
a very familiar feature is visible -
the gas and dust clouds which line the plane of our galaxy
absorb x-rays as well
as optical light and produce
the dark bands running through the
galactic center.
APOD: September 18, 1996 - Stars in the Infrared Sky
Explanation:
What if you could see
infrared light?
Because this light is less
absorbed by dust
than visible light, you could
peer into the center of our Milky Way Galaxy. The stars there are
normally hidden from direct view by
the interstellar dust clouds which
line the Galactic plane.
Above is a false color image of the entire sky made by
the DIRBE instrument onboard
NASA's COBE Satellite using
infrared light with a wavelength of 3.5 microns
- about 7 times longer than the wavelength of visible light.
The galactic plane runs horizontally along the middle of the image.
At this wavelength, the
cool stars in our galaxy shine brightly and can be seen to define the
plane of the Milky Way and the central bulge.
Interplanetary dust,
which tends to lie along the plane of our
own solar system, scatters sunlight and emits radiation at these
wavelengths too.
The faint glow it produces results in the
"S" shape apparent in this infrared all-sky view.
APOD: August 12, 1996 - Leo Triplet Spiral Galaxy M65
Explanation:
Spiral galaxy M65 is a normal spiral galaxy not unlike our own Milky Way.
In fact,
M65
is a typical
spiral galaxy of a type that could be found
anywhere in the local universe. Given a morphological type of "Sa", M65
shows tightly wrapped spiral arms and a large nuclear central bulge. The
central bulge stars are older and redder than disk stars, which appear more
blue. Stars in the bulge of the our own
Milky Way Galaxy are also
typically older and redder than stars in the disk where our
Sun resides. M65 is a member of the
Leo
Triplet of galaxies, along with its neighbors
M66 and
NGC
3628. Although it appears that M65's gravity has distorted M66's
symmetry, M65's symmetry seems unaffected by M66. M65 is located roughly 35
million light years away, so that light recorded today left after the fall
of the dinosaurs but when many land mammals were just evolving on
Earth.
APOD: July 23, 1996 - Hale-Bopp, Jupiter, and the Milky Way
Explanation:
Shining brightly,
the mighty Jupiter rules this gorgeous
Kodacolor photo of
the Milky Way near Sagittarius.
Astronomer Bill Keel took the picture earlier this month (July 7)
while standing near the summit of
Hawaii's Mauna Kea
contemplating the sky in the direction of the
center of the Galaxy (right of picture center).
In addition to the gas giant planet, which
is well placed for evening viewing,
the image contains an impressive sampler of celestial goodies.
Many famous emission nebulae
are visible as reddish patches -
M16, the Eagle nebula,
is just above and right of center, with
the Horseshoe nebula, M17, just below it and farther to the right.
Also, look for the Lagoon Nebula, M8, as
the brightest red patch at the right of the picture with
the Trifid Nebula, M20,
just above it and to the left.
The milky glow of distant unresolved stars
in the plane of our Galaxy (thus the term Milky Way) runs through
the image cut by dark, absorbing, interstellar
dust clouds.
The much anticipated
comet Hale-Bopp is also clearly visible. Where's the
comet? Click on the picture to view the comet's location
flanked by superposed vertical lines.
The comet was discovered while
still beyond the orbit of Jupiter
a year ago today independently by
Alan Hale
and Thomas Bopp. Astronomers monitoring
Hale-Bopp's activity report that
having now brightened to almost 6th
magnitude
it is still on track for becoming
an extremely bright naked-eye comet in early 1997.
APOD: July 9, 1996 - M74: A Grand Design Spiral Galaxy
Explanation:
M74 is about the same size as our own Milky Way Galaxy. Like our
Milky Way,
M74 is classified
a spiral galaxy. M74's sweeping lanes of
stars and
dust combined with its
small nucleus make it a classic
Grand
Design Spiral. On the
Hubble Sequence of Galaxies, M74 is listed as "Sc".
In the
above picture, visible light is shown in red and
ultraviolet light
superposed in blue. In general, older stars are more red and younger
stars are blue.
Studies with the Ultraviolet Imaging Telescope show that the disk of M74 has undergone significant star formation in just
the past 500 million years.
APOD: July 8, 1996 - M33: The Triangulum Galaxy
Explanation:
The spiral galaxy
M33
is a mid-sized member of our
Local Group of galaxies.
M33 is also called the Triangulum Galaxy for the constellation in which it resides.
About four times smaller (in radius) than our
Milky Way Galaxy and the
Andromeda Galaxy
(M31), it is much larger than the many of the
local dwarf spheroidal
galaxies. M33's proximity to M31 causes it to be thought by some to be a
satellite galaxy of this more massive galaxy. M33's proximity to our Milky
Way galaxy causes it to appear more than twice the angular size of the
full moon, and visible with a
good pair of
binoculars.
In the
above picture, visible light is shown in red and
ultraviolet light
superposed in blue.
Stars in M33 are the most distant ever to be studied
spectroscopically.
APOD: June 5, 1996 - Sagittarius and the Central Milky Way
Explanation:
What does the center of our
Milky Way Galaxy look like? No one knows! It
is not possible to see the Galactic center in light our eyes are sensitive
to because the thick
dust in the
plane of our Galaxy obscures it. If one
looks in the direction of our Galaxy's center - which is toward the
constellation of Sagittarius - many beautiful wonders become apparent,
though. The center of the Milky Way is behind the center of the photo.
Large dust lanes and star clouds dominate the picture.
As many as 30
Messier Objects
are
visible, including all types of nebula and star
clusters. Two notable nebula include the
Lagoon Nebula (M8), a small red
patch just above center, and slightly above this is the red and blue
Trifid
Nebula (M20). The lines through picture were caused by airplanes, and the
dark objects in the foreground are trees.
APOD: May 19, 1996 - Nearby Dwarf Galaxy Leo I
Explanation:
Leo I is a
dwarf spheroidal
galaxy in the
Local Group of galaxies dominated
by our
Milky Way Galaxy and
M31. Leo I is thought to be the most distant of
the eleven known small
satellite galaxies orbiting our
Milky Way Galaxy.
Besides the
LMC and the
SMC, all Milky Way satellite galaxies are
small,
dim, dwarf spheroidals, including the closest galaxy - the
Sagittarius
Dwarf. Leo I is most distant than most of them, thought to be about 250
kpc away. Analysis of stars in Leo I show it contains many stars only about
3 billion years old - much younger than in most galaxies.
APOD: May 15, 1996 - The Milky Way Near the Northern Cross
Explanation:
This beautiful image of the sky near the bright star
Deneb
(just above center) reveals the stars, nebulae, and dark clouds
along the plane of our Milky Way Galaxy as seen from the northern
hemisphere (near Columbia Missouri, USA).
Just below Deneb lies the suggestively shaped North America emission nebula.
Deneb is
the brightest star in the constellation
Cygnus,
located in the tail of this
celestial swan.
Cygnus
contains the asterism known as the Northern Cross and
marks one side of the "Great Rift" in the Milky Way, a series of dark
obscuring dust clouds which stretches on through the constellation
Sagittarius.
Deneb defines the top of the Northern
Cross while the body of the cross extends past the
upper right corner of the picture.
Cygnus also harbors the most famous
candidate for a black hole in our galaxy,
Cygnus X-1.
APOD: May 3, 1996 - The Milky Way Near the Southern Cross
Explanation:
This breathtaking patch of sky would be above you were you to stand at the
south pole of the Earth.
Just above and to the right of the photograph's center are the four stars
that mark the boundaries of the famous
Southern Cross.
At the top of this constellation, also known as "The Crux,"
is the orange star
Gamma Crucis.
The band of stars, dust, and gas crossing the middle of the photograph is
part our
Milky Way Galaxy.
In the very center of the photograph is
the dark Coal Sack Nebula, and the bright nebula on the far right is the
Eta Carina Nebula.
The southern cross is so famous a constellation that it is depicted on the
Australian National Flag.
APOD: February 13, 1996 - 7,000 Stars And The Milky Way
Explanation:
This panorama
view of the sky is really a drawing.
It was made in the 1940s under the supervision of astronomer Knut Lundmark at
the Lund Observatory
in Sweden. To create the picture, draftsmen used
a mathematical distortion to map
the entire sky onto an oval shaped image with
the plane of our Milky Way Galaxy
along the center and the north galactic
pole at the top. 7,000 individual stars are shown as white dots, size
indicating brightness. The "Milky Way" clouds, actually the combined
light of dim, unresolved stars in the densely populated galactic plane, are
accurately painted on, interrupted by
dramatic dark dust lanes.
The overall effect is photographic in quality and represents the visible
sky. Can you identify any familiar landmarks or constellations?
For starters,
Orion
is at the right edge of the picture, just below the galactic plane
and the Large and
Small Magellanic Clouds are visible as
fuzzy patches in the lower right quadrant.
APOD: February 5, 1996 - COBE Dipole: Speeding Through the Universe
Explanation:
Our Earth is not at rest.
The Earth moves around the Sun.
The Sun orbits the center of the Milky Way Galaxy.
The Milky Way Galaxy orbits in the
Local Group.
The Local Group falls toward the
Virgo Cluster of Galaxies.
But these speeds are less than the speed that all of these objects together
move relative to the
microwave background.
In the above all-sky map, radiation in the Earth's direction of motion appears
blueshifted and hence hotter, while radiation on the opposite side of the
sky is redshifted and colder. The map indicates that the Local Group
moves at about 600 kilometers per second relative to this
primordial
radiation. This high speed was initially unexpected and its magnitude
is still unexplained. Why are we moving so fast? What is out there?
APOD: February 4, 1996 - The Closest Galaxy: The Sagittarius Dwarf
Explanation:
What's the closest galaxy to our Milky Way?
For many years astronomers thought it was the
Large Magellanic Cloud (LMC). But the
seemingly insignificant fuzzy patch shown above turned out to be part of a
galaxy that is even closer. Deemed the
"Sagittarius Dwarf",
this small galaxy went unnoticed until its discovery in 1994 by R. Ibata,
G. Gilmore and M. Irwin
(RGO).
The reason the Sagittarius Dwarf hadn't been discovered earlier is because
it is so dim, it is so spread out over the sky, and there are so many Milky
Way stars in front of it. The distance to the Sagittarius Dwarf was
recently measured to be about one third of the distance to the LMC.
Astronomers
now believe that this galaxy is slowly being torn apart by the
vast gravitational forces of our Galaxy.
APOD: February 1, 1996 - Lensing through Baade's Window
Explanation:
What is the shape and composition of our
Milky Way Galaxy? This question
would be easier to answer if there wasn't so much obscuring
dust! In the
1940s, however, astronomer
Walter
Baade identified a "window" near the
center of our Galaxy where there is comparatively little opaque dust. Now
called
"Baade's
Window", this sky region contains millions of stars and is
used for many studies of the distant
Milky Way. One clever use, devised by
Bohdan Paczynski, is to monitor millions of stars in our Galactic Bulge -
many through Baade's window - for
sudden brightening due to
gravitational
lensing. Current observations by the
OGLE and
MACHO
collaborations have now identified dozens of gravitational amplification
events. This unexpectedly large number supports previous claims that
our Galaxy
has a "bar" of stars across the central nucleus, pointed nearly at the
Sun.
APOD: October 29, 1995 - Radioactive Clouds in the Milky Way
Explanation:
When massive stars explode
they create large radioactive
blast clouds which expand into interstellar space.
As the radioactive elements decay, they produce
gamma-rays. Possible locations of these stellar explosions
known as supernovae,
are indicated by the bright clumps
in this map of the central regions of our Milky Way Galaxy.
The map was made by a telescope onboard NASA's orbiting
Compton Gamma Ray Observatory
using detectors sensitive to
gamma rays from the decay of radioactive aluminum.
APOD: September 19, 1995 - The Small Cloud of Magellan
Explanation:
Almost unknown to casual observers in the northern hemisphere,
the southern
sky contains two diffuse wonders known as the
Magellanic Clouds.
The Magellanic Clouds are small irregular
galaxies orbiting our
own larger Milky Way spiral galaxy.
The Small Magellanic Cloud
(SMC), pictured here,
is about 250,000 light years away and
contains a preponderance of young, hot, blue stars indicating it has
undergone a recent period of star formation.
There is evidence that the SMC is actually two
galaxies superposed to appear as one.
The bright blob near
the right hand edge of the frame is a
globular cluster near the
outskirts of the Milky Way.
APOD: September 18, 1995 - The Large Cloud of Magellan
Explanation:
Magellan and his crew had plenty of time to study the southern sky
during their famous voyage around the world. As a result, two fuzzy
cloud like objects, nestled among the southern constellations of Doradus
and Tucana are now
known as the Clouds of Magellan. The Magellanic Clouds are small irregular
galaxies, satellites of our
larger Milky Way spiral galaxy.
The Large Magellanic Cloud
(LMC) pictured above is the closest galaxy to our own Milky Way,
at a distance of about 180,000 light years.
The Magellanic Clouds are joined to the Milky Way by a
stream of cold hydrogen gas whose origin is still controversial.
An unusual effect called
gravitational lensing has recently
been detected in a few LMC stars, and there is hope this could
tell us important information about the
true composition of our universe.
APOD: September 8, 1995 - The Milky Way's Center
Explanation:
NASA's
COBE satellite scanned the heavens at infrared wavelengths in
1990 and produced this premier view of the central region of our own Milky Way
Galaxy. The Milky Way is a typical spiral
galaxy with a central bulge and extended disk of stars. However, gas
and dust
within the disk obscure visible wavelengths of light effectively
preventing clear observations of the center. Since infrared
wavelengths, are less affected by the obscuring material, the
Diffuse InfraRed Background Experiment (DIRBE)
on board COBE was able to
detected infrared light from stars surrounding the galactic center and
produce this image.
Of course, the edge on perspective represents
the view from the vicinity of our Sun,
a star located in the disk about 30,000 light years out from the center.
The DIRBE experiment used equipment cooled by a tub
of liquid helium to detect the infrared light which, composed of wavelengths
longer than red light, is invisible to the human eye.