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-3/2 relationship: The special mathematical relationship between the number of objects detected with brightness larger than some value and the brightness itself. If found, this relationship indicates that the sources are distributed in a manner consistent with a uniform density.

Aerogel: A nearly transparent, very lightweight material made primarily from silica. Dubbed a "Super Material", aerogel is the world's lightest solid, weighing as little as three times that of air, and exhibiting superb insulating properties.

Acceleration: The rate at which an object's velocity changes with time.

Angstrom: A unit of length equivalent to one hundred-millionth of a centimeter. See electromagnetic spectrum.

Anisotropic: Not Isotropic; Not randomly distributed

AXAF: (Advanced X-Ray Astrophysics Facility) One of NASA's Great Observatories, an X-Ray telescope designed to perform astronomy from low Earth orbit.

BATSE: (Burst and Transient Source Experiment) contributed by Marshall Space Flight Center, this is one of the four experiments on the Compton Gamma Ray Observatory .

Big Bang: Event that cosmologists consider the beginning of the universe, in which all matter and radiation in the entire universe came into being.

Blue Shift: A term used to describe the apparent increase in frequency that an observer detects due to relative motion between the source and the observer, such that the two are getting closer together.

Buoyancy-Driven Convection: Convection created by the difference in density between two or more fluids in a gravitational field.

Brightness Distribution: A graph of the number of bursts observed at each brightness level.

COMPTEL: (Compton Telescope) contributed by European Space Agency (ESA), this is one of the four experiments on the Compton Gamma Ray Observatory .

Convection: Energy and/or mass trasfer in a fluid by means of bulk motion of the fluid. (e.g. heating water on the stove causes the hotter water on the bottom to rise, mixing with the cooler water on top.)

Diffusion: Intermixing of atoms and/or molecules in solids, liquids, and gases due to a difference in composition.

Dispersion Formation: (Microgravity Science) fine droplets of one metal dispersed in another metal

Doppler-shift: Any motion-induced change in the observed wavelength (or frequency) of a wave.

Drop Tower/Drop Tube: Research facility that creates a microgravity environment by permitting experiments to free fall through an enclosed vertical tube.

Ecliptic: The plane in space which contains the Sun, Earth, and the other major planets.

EGRET: (Energetic Gamma-ray Experiment Telescope) One of the four experiments on the Compton Gamma Ray Observatory .

Electromagnetic Spectrum: The entire range of radiation extending in frequency from 10²³ cycles per second (or Hertz) to zero Hertz. Diagram.

Electron-Volts: Unit of energy equal to that attained by an electron falling unimpeded through a potential difference of one volt.

ESA European Space Agency.

Exothermic: Releasing heat.

Fluid: Anything that flows, either liquid or gas. Some solids can also exhibit fluid behavior over time.

Free fall: Falling in a gravitational field where the acceleration is the same as that due to gravity alone.

G: The universal gravitational constant (6.67x10^-11 Nm²/kg²)

g: The acceleration Earth's gravitational field exerts on objects at Earth's surface. (9.8 m/sec²)

Galactic Coordinates: Sky location coordinates given with respect to the center of the Milky Way Galaxy (our galaxy). The Milky Way galaxy is a spiral galaxy - very flat with a bulging core. Galactic coordinates are expressed in galactic latitude and galactic longitude. Galactic latitude is measured from the galactic equator north (positive numbers) or south (negative numbers); galactic longitude is measured eastward along the galactic plane from the galactic center. From Earth, the center of the galaxy is in the constellation Sagittarius. The galactic plane lies along the 0° latitude. Diagam.

Galactic disk: The flattened region of gas and dust in which one finds the arms of a spiral galaxy.

Galactic halo: The region of a galaxy extending far above and below the galatic disk, where globular clusters and other old stars reside.

Gamma-Ray Bursts: Brief flashes of highly energetic photons (light) that occur at random times and unpredictable locations in the sky. A gamma-ray burst might look light a flash from a flashlbulb, if the human eye could detect this type of light. See Electomagnetic Spectrum diagram to see the relationship between gamma radiation and visible light. Also check out this animation , simulating a gamma-ray burst as viewed by a satellite.

GINGA: Japanese X-Ray and Gamma-Ray spacecraft

GOES: Geostationary Operational Environmental Satellite

GOSAMR: Gelation Of Sols: Applied Microgravity Research. This experiment was flown as a standard payload as part of a series of microgravity materials processing
experiments in 1991 on board STS-42. Reflight in 1998 is planned.

GRANAT: Russian X-Ray and Gamma-Ray spacecraft.

Gravitation: The attraction of object due to their masses.

Homogeneous: - The same in structure and quality; similar or identical.

Hubble Constant: - The constant of proportionality which gives the relation between apparent recessional velocity and distance in Hubble's law.

Hydrostatic pressure: The pressure which is exerted on a portion of a column of fluid as a result of the weight of the fluid above it.

Inertia: A property of matter that causes it to resist changes in speed or direction (velocity).

Interplanetary Triangulation: Triangulation is used to determine the location of an unknown point, by forming a triangle having the unknown point and two known points at the three verticies. Interplanetary triangulation extends this concept to determining the location of a point in space by using orbiting spacecraft as the two known points of the triangle.

Isotropic: Having physical properties that are the same regardless of the direction of measurement. Opposite of anisotropic.

ISO-9000: International Standards Organization set of standards given the numeric "9000". This set of standards is used by businesses to ensure manufacture of quality products.

KC-135: A modified Air Force KC-135 (70 KB jpeg picture) aircraft used by NASA for astronaut training and short-duration low-gravity scientific research.

keV: A unit of energy equal to one thousand electron volts.

Law of Universal Gravititation: A law that states that every mass in the universe attracts every other mass with a force proportional to the product of their masses and inversely proportional to the square of the distances between their centers.

Light-year: A unit of length equal to the distance that light travels in one year, approximately 5.8 trillion miles.

Luminosity: The total amount of energy per unit time released by an object.

Mass: A basic property of matter. It is a measure of an object's resistance to acceleration. On Earth's surface, an object's mass is different from, but proportional to, its weight.

M31 (Andromeda): The nearest large spiral galaxy to our own Milky Way Galaxy

Magellanic Clouds: Two nearby, small, irregular galaxies that are gravitationally bound to the Milky Way Galaxy and visible to the naked eye from the southern hemisphere.

Main Sequence: The stable phase of a star's lifetime, when outward pressure from internal fusion process using hydrogen for fuel is balanced by the inward force of self-gravitation. This phase is usually the longest phase of a star's lifetime. Our Sun is a main sequence star.

Microgravity: Microgravity is a term commonly applied to a condition of free-fall within a gravitational field in which the weight of an object is reduced compared to its weight at rest on Earth.

Monomer: (Chemistry) Any molecule that can be chemically bound as a unit of a polymer.

Neutron Star: A collapsed star of extremely high density. Generally these objects have slightly more mass than the Sun, but are only about 10 km in radius. A neutron star has intense gravity, and may also have an intense magnetic field and fast rotational component.

Oort Cloud: The spherical region around the Sun thought to contain a large number of cometary bodies.

OSSE: (Oriented Scintillation Spectrometer Experiment) One of four experiments on the Compton Gamma Ray Observatory.

Parabolic Flight Path: The flight path followed by airplanes in creating a microgravity environment (the shape of a parabola).

Peak Flux: A measure of a burst's intensity, this quantity has units of energy per unit area per unit time.

pH: (Potential of Hydrogen) In chemistry, a measure of the acidity or alkalinity of a solution, numerically equal to 7 for neutral solutions, increasing with increasing alkalinity and decreasing with increasing acidity.

Photon: The quantum of electromagnetic energy, generally regarded as a discrete particle having zero mass, no electric charge, and an indefinitely long lifetime. See Electromagnetic Spectrum.

Polymer: (Chemistry) Any of numerous natural and synthetic compounds of usually high molecular weight consisting of up to millions of repeated linked units, each a relatively light and simple molecule. (see monomer)

Pulsar: A neutron star with a very fast rotational component and strong magnetic field, which constrains emitting radiation to a cone. To be visible from Earth, a pulsar must be oriented such that the cone of emitted radiation intersects Earth. Tutorial.

Quasar: abbreviation of "quasi-stellar object". Quasars are unusually energetic objects which emit up to 1,000 times as much energy as an entire galaxy, but from a volume about the size of our solar system.

Rayleigh: A rayleigh = 10⁶ photons emitted in all directions per cm2 vertical column per second. Rayleighs are used to measure the luminous intensity of the aurora.

SIRTF: Space Infrared Telescope Facility

Skylab: NASA's first orbital laboratory that was operated in 1973 and 1974.

Soft Gamma Repeaters: Objects believed to be related to a particular type of supernova remnant and/or its associated neutron star which emit soft "pops" of gamma-ray energy in short intense bursts. Detectable by BATSE, but different from the "classical" gamma-ray burst.

Solar Radius: 697,000 kilometers (436322 miles)

Spacelab: A scientific laboratory developed by the European Space Agency that is carried into Earth orbit in the Space Shuttle's payload bay.

International Space Station: planned for operation in the 1990's.

Stratosphere: The portion of the Earth's atmosphere ranging from approximately 14 km to 22 km (8 to 12 miles). Diagram.

Super materials: Super materials include crystals, semiconductors, nanotechnology, superalloys and metals, high performance glasses, gels, polymer thin films, and superconductors processed and produced using innovative techniques. The scientific study of super materials incorporates parts of traditional materials science disciplines with biotechnology, physics and chemistry. Primary uses include lasers, medical imaging, and pharmaceuticals. Theme.

Supernova: A supermassive star may undergo a cataclysmic explosion at some point after it has exhausted its internal hydrogen used for fuel. The famous crab nebula is a beautiful example of the still-expanding gases surrounding a supernova explosion that occurred in the year 1054.

TIROS: Television and Infrared Observation Satellite

Troposphere: The portion of the Earth's atmosphere ranging from the Earth's surface to approximately 14 km (0 to 8 miles). Diagram.

Velocity: Distance travelled per unit time. E.g. miles per hour, feet per second, etc.

Visible Light: That portion of the electromagnetic spectrum which is detectable by the human eye. The sun emits "white" light, which is all visible colors, but which is only a small part of the entire electromagnetic spectrum. Visible light is energy in the range of approximately 7800 to 3900 Angstroms, where one Angstrom is 0.0000000001 meters. The visible spectrum is most obvious in a rainbow, when the sun's different colors of light are bent (refracted) by the earth's atmosphere during a rainstorm. Diagram.

Watt: A unit of power, equivalent to one joule of energy per second.

Wavelength: The distance between successive crests or troughs in a wave.