Artificial satellites - Man-made satellites which orbit our planet

Asteroid - Any of numerous small celestial bodies that revolve around the sun, with orbits lying chiefly between Mars and Jupiter and characteristic diameters between a few and several hundred kilometers

Black hole - An extremely small region of space-time with a gravitational field so intense that nothing can escape, not even light

coma - The nebulous, luminescent cloud containing the nucleus and constituting the major portion of the head of a comet.

comet - A celestial body, observed only in that part of its orbit that is relatively close to the sun, having a head consisting of a solid nucleus surrounded by a nebulous coma up to 2.4 million kilometers (1.5 million miles) in diameter and an elongated, curved vapor tail arising from the coma when sufficiently close to the sun. Comets are thought to consist chiefly of ammonia, methane, carbon dioxide, and water.

fusion - A nuclear reaction in which nuclei combine to form more massive nuclei with the simultaneous release of energy

meteor - A bright trail or streak that appears in the sky when a meteoroid is heated to incandescence by friction with the earth's atmosphere. Also Called falling star

meteorite - stony or metallic mass of matter that has fallen to the earth's surface from outer space

meteor shower - A large number of meteors that appear together and seem to come from the same area in the sky.

nebula - A diffuse mass of interstellar dust or gas or both, visible as luminous patches or areas of darkness depending on the way the mass absorbs or reflects incident radiation.

nova - A star that suddenly becomes much brighter and then gradually returns to its original brightness over a period of weeks to years.

outer planets - Any of the five planets, Jupiter, Saturn, Uranus, Neptune, and Pluto, with orbits outside that of Mars.

photosynthesis - The process in green plants and certain other organisms by which carbohydrates are synthesized from carbon dioxide and water using light as an energy source. Most forms of photosynthesis release oxygen as a byproduct.

plate tectonics - A theory of global dynamics having to do with the movement of a small number of semirigid sections of the earth's crust, with seismic activity and volcanism occurring primarily at the margins of these sections. This movement has resulted in continental drift and changes in the shape and size of ocean basins and continents.

satellites - A celestial body that orbits a planet; a moon

Solar system - The sun together with the nine planets and all other celestial bodies that orbit the sun.

Solar wind - A stream of ionized particles ejected at high speeds from the surface of the sun.

Super nova - A rare celestial phenomenon involving the explosion of most of the material in a star, resulting in an extremely bright, short-lived object that emits vast amounts of energy.

Terrestrial planets - Any of the four planets, Mercury, Venus, Earth, or Mars, that are nearest the sun and have similar size and density.