| A | B |
|---|
| Solar system | the sun together with all the planets and other bodies that revolve around it |
| Planet | any of the nine large heavenly bodies revolving about the sun and shining by reflected light: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, or Pluto in the order of their proximity to the sun |
| Solar nebula | Also called diffuse nebula. a cloud of interstellar gas and dust |
| Eccentricity | an oddity or peculiarity, as of conduct |
| Orbital period | the time taken for a given object to make one complete orbit about another object |
| Inertia | the property of matter by which it retains its state of rest or its velocity along a straight line so long as it is not acted upon by an external force |
| Terrestrial planet | any of the four planets, Mercury, Venus, Earth, or Mars, that are nearest the sun and have similar size and density |
| Gas giant | any of the four outermost planets in the solar system; much larger than Earth and gaseous in nature |
| Biosphere | the part of the earth's crust, waters, and atmosphere that supports life |
| Lithosphere | the crust and upper mantle of the earth, the solid portion of the earth |
| Mare | any of the large dark areas on the moon or on Mars or other planets |
| Regolith | layer of loose rock resting on bedrock, constituting the surface of most land |
| Terrae | rough upland or mountainous region of the moon with a relatively high albedo |
| Meteorite | a mass of stone or metal that has reached the earth from outer space; a fallen meteoroid |
