Absolute Magnitude

The measure of how bright a star would be located 10 parsecs from earth.

Absorption Spectrum

A continuous spectrum crossed by dark lines produced when light passes through a non-incandescent gas.

Apparent Magnitude

The measure of how bright a star appears to be to an observer on earth.

Astronomical Unit (AU)

The average distance between earth and the sun, about 150 kilometers.

Big Bang Model

The theory holding that the universe originated from the instant expansion of an extremely small agglomeration of matter of extremely high density and temperature.

Black Hole

The final life stage  of an extremely massive star, with a gravitational field so intense that not even light can escape.

Cepheid variables

A variable star  that brightens and dims regularly, or pulses, and whose distance can be determined from its period of pulsation.

Constellation

A group of stars that appear to form a pattern in the sky.

Doppler Effect

The apparent change in the wavelength of radiation or of sound in which there is relative motion between the source and the receiver.

Electromagnetic spectrum

A continuum depicting the range of electromagnetic radiation, with the longest wavelength at one end and the shortest at the other.

Emission spectrum

A spectrum consisting of individual lines at characteristic wavelengths produced when light passes through an incandescent gas; a bright light spectrum.

Giant Star

A large star with great luminosity and a diameter 10 to 100 times greater than that of the sun.

Light Year

The distance that light travels in one year, about 9.5 trillion kilometers.

Luminosity

The brightness of the star.

Main Sequence Star

A star that is at the point in its life cycle in which it is actively fusing hydrogen nuclei into helium nuclei.

Nebula

A large cloud of gas and dust in space.

Neutron star

The super dense remains of a massive star that collapsed with enough force to push all of its electrons into the nuclei they orbit, resulting in a mass of neutrons.

Parallax

The apparent shift in one objects position relative to another caused by a change in the location of the observer.

Parsec

A unit of measurement used to describe distances between celestial objects, equal to 3.258 light-years.

Planetary nebula

A halo of gases that is formed by the expelled layers of a star's atmosphere.

Pulsar

A distant neutron star that emits rapid pulses of light and radio waves instead of steady radiation.

Quasar

A very distant, extremely luminous celestial object that scientists consider to be a type of active galactic nuclei.

Supernova

The brilliant burst of light that follows the collapse of the iron core of a massive star.

White Dwarf

The remnant of a giant star that has lost its outer atmosphere, the glowing stellar core.