| Term | Definition |
| solar system | the Sun and all the bodies that orbit it |
| revolution | one full orbit of an object around another object |
| axis | an imaginary center line around which the Earth roatates |
| rotation | one whole spin of an object on its axis |
| space probe | a spacecraft that gathers data without a crew |
| comet | a frozen mass of ice and dust orbiting the Sun |
| asteroid | a rocky mass up to several hundred kilometers wide that revoluves around the Sun |
| satellite | an object in orbit around another object |
| moon phase | an indication of the fraction of the Moon that is illuminated as seen from Earth |
