Elliptical Galaxy - A system of stars that contains little dust and gas and may be composed of millions to trillions of stars.
Main Sequence Star - A star that lies along a diagonal from upper left to lower right on the Hertzsprung-Russell diagram; uses up its hydrogen fuel at a steady rate.
Big Bang - A theory stating that the universe originated from the explosion of a huge mass of matter, which cooled, collected into clouds, and formed galaxies.
Reflecting Telescope - An instrument in which light is collected, reflected, and focused by a concave mirror and the image formed is magnified in the eyepiece.
Absolute Magnitude - A measure of a star's actual brightness.
Fusion - The process of two low mass nuclei being joined to form one nucleus; the source of a star's light and thermal energy.
Nebula - A low density cloud of gas and dust in which a star is born.
Expanding Universe - Theory that states the universe is currently expanding and shall continue to do so.
Refracting Telescope - An instrument that uses an objective lens to bend light toward the focal plane where the image is formed.
Spiral Galaxy - A disk-shaped galaxy with arms that rotates round a dense center.
Light-Year - A measure of the distance light travels in one year, which equals to 9.5 X 10 (to the 12th power) km.
Constellations - Group or pattern of stars.
Radio Telescopes - An instrument consisting of a reflector, a receiver, and an antenna used to collect radio waves from space.
Spectroscopes - An instrument that separates visible light into its various wavelengths.
Irregular Galaxy - Galaxy that contains clouds of gas and dust and stars that are in the early stages of their life cycles.
Black Holes - A star in which matter is condensed and its gravity field is so strong that light cannot escape.
Red Shift - Observed shift in light wavelengths occurring when a light source is moving away from an observer.
