| 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 |