Astronomy Dictionary

Apogee - The point in its orbit around the earth at which an object is furthest from the Earth.

Asteroid - Any of the thousands of small planets or Minor Planets.

Aurora - Glows seen over the polar regions which occur when energized particles from the Sun react with particles from the Earth .

Axis - An imaginary straight line on which an object rotates.

Black Hole - A region of space around a very small and extremely massive collapsed star within which the gravitational field is so intense that not even light can escape.

Comet - A small, frozen mass of dust and gas revolving around the sun in an ellipitical orbit.

Constellation - A grouping of stars which many times form a shape or pattern.

Eclipse - The hiding or blocking of one celestial object from another.

Galaxy - A huge collection of stars, gas and dust measuring many light years across.

Light Year - The distance which a ray of light would travel in one year. This is about 6,000,000,000,000 (6 trillion) miles.

Meteor - The luminous phenomenom observed when a meteoroid is heated by its entry into the Earth's atomsphere.

Meteorite - That part of a relatively large meteoroid that survives passage through the atomsphere and falls to the surface of a planet as a mass of metal or stone.

Milky Way - The spiral galaxy containing our Sun. As seen from Earth, the constellation Sagittarius marks the direction to its center.

Nadir - That point on the celestial sphere directly opposite the zenith and directly below the observer. The lowest point.

Nebula - An interstellar cloud of gas and dust.

Nova - A star which suddenly flares up to many times its original brightness before fading again.

Orbit - The closed path of one object around another.

Perigee - The point in its orbit around the Earth at which an object is closet to the Sun.

Revolve - To cause to travel in a circle or orbit.

Rotate - To turn about a center point or axis.

Satellite - A small object orbiting a larger one.

Sidereal Period - The time it takes one object to complete one orbit around another.

Solar System - The description given to the system dominated by the Sun and including the Planets, Minor Planets, Comets, planetary satellites and interplanetary debris that travel in orbits around the Sun.

Star - A self-luminous object that shines through the release of energy produced by nuclear reactions at its core.

Supernova - A huge stellar explosion involving the destruction of a massive star and resulting in a sudden and tremendous brightening.

Zenith - The point in the sky directly above the observer. The highest point.