Absolute Magnitude (M) - The magnitude that a celestial object would appear to have at a distance of 10 parsecs. i.e. it is independent of the actual distance from us obversers on earth. See also: Magnitude

Absulote Visual Magnitude M_v - The absolute magnitude of a celestial object measured with a device that simulates the way things are seen through the human eye. See also: Magnitude

Absorbtion Nebula - A nebula that is seen as a dark cloud or silhouette as it absorbs light from behind. See also: Emission Nebula

Apparent Magnitude - The magnitude of a celestial object as seen by an observer. See also: Magnitude

Astrophysicist - a person that studies the physics of stellar phenomena.

Binary Star - A double star; a system containing two or more stars, locked in constant orbit. In an eclipsing binary, one star goes behind the other periodically, changing the total amount of light we can see.

Black Hole - A region of space in which the density is so great that nothing, not even light can escape. To learn more about black holes, try our article in the info section.

Centrifugal - moving or directed away from a center or axis.

Coincidedy - to occupy the same position simultaneously.

Conglomerate - a collected heterogeneous mass : Cluster.

Constellation - The night sky has been divided into eighty-eight of these, each a group of bright stars that refers to a historical or mythilogical figure.

Degenerate - having declined, as in nature or function from a former original state.

Degeneracy - the state of being degenerate.

Disillusionment - the act of disenchanting, especially to disappoint or embitter by leaving without illusion.

Double Star - A system containing two or more stars. In many double star systems, the stars are not actually physicall close to eachother, they only appear to be beacuse of the way we view the sky. True double stars are called binary stars. See also: binary star, of course.

Electrons - a subatomic particle particle in the lepton family. The most basic negative charge.

Emission Lines - Extra radiation at certain specific wavelengths in a spectrum, compared with neighboring wavelengths. These designate the presence of hot gas surrounding a star.

Emission Nebula - A gas cloud that receives energy from a hot star, allowing it to give off radiation in emission lines. These nebula are often very beatiful to look at. Many nebulae are both emission and absorbtion. Some examples are the Horsehead Nebula and the North America Nebula. See also: Absorbtion Nebula.

Emit - to send or give out.

Galaxy - A giant collection of stars, gas, and dust. Most stars in the universe are in galaxies. Nearly all of the stars visible in the night sky are within our own galaxy, the Milky Way. Most of the objects that are visible outside of our galaxy are other galaxies.

Gamma - a gamma ray.

Gamma Ray - electromagnetic radiation with energy greater than several hundred thousand electron volts.

Giant - A star that is espcially bright and large for its color/temperature. Many stars become red giants late in their life and some even become supergiants. For more information on these phenomenae, view our Birth and Death of a Star article at the Information Realm.

Globular ClusterA spherical cluster of stars of a common origin. These stars and clusters are often very old.

Interstellar - among or between the stars.

Kelvin - of or relating to an absolute scale of temperature whose zero point is approximate -273.16^oC

Light Year - Despite its odd name, a light year is a measure of distance, not time. It actually designates the distance that light can travel in one year, which equals 9,460,000,000,000 km.

Magnitude - A scale on which the brightness of a star is measured. This scale is logarithmic, meaning each successive magnitude is increasingly brighter/dimmer than the last. To be more precise, each change of five magnitudes is equivalent to a change by a factor of 100. Also, stars with a lower magnitude are the brightest. Stars may have negative magnitudes. For example, a star with a magnitude of -1 is 100 times brighter than one of a magnitude of 4. See also: Absoulte Magnitude, Absolute Visual Magnitude, and Apparent Magnitude.

Main-sequence star - A star in the main cycle of its life, where hydrogen inside is undergoing nuclear fusion. Most of the stars that we see in the sky at night are main sequence stars. You can learn about a star's main sequence at the Main Sequence page.

Neutron - an electrically neutral subatomic particle in the baryon family, having a mass 1,839 times that of the electron, stable when bound in an atomic nucleus, and having a mean lifetime of approximately 16.6 min. as a free particle.

Parsec - The distance from which one astronomical unit appears to cover. More importantly, a parsec equals 3.261633 light years.

Proton - a stable, positively charged subatomic particle in the baryon family with a mass 1,836 times that o the electron.

Radio Astronomy - study of celestial bodies and phenomena by observation and analysis of their associated radio-frequency emissions.

Quasar - a quasi-stellar radio source. These peculiar objects emit radio waves with a large redshift. The redshift represents the fraction of the percentage in which the wavelengths are switched. Quasars are very far away, and very bright, and many astronomers agree that giant black holes are present within these objects. See also: black hole.

Synchrotron - an accelerator in which charged particles are accelerated around a fixed circular path by a radic-frequency potential and held to the path by a time-varying magnetic field.

Variable Star - A star whose apparent brightness changes over this. This is due to a change in the stars mass/size. See also: binary star, apparent brightness.

Wavelength - the distance in a periodic wave between two points of corresponding phase in consecutive cycles.

Zodiac - Traditionally, a set of 12 constellations through which the sun, moon, and planets pass through in a year. Many of the brightest stars of the night sky are in these constellations.

A.U. - astronomical unit

^oC - degrees celsius

g/cm³ - grams per cubic centimeter

kg - kilogram

km - kilometer

km/sec - kilometer per second