| A | B |
|---|
| revolving | turning or spinning |
| hollow | empty; nothing inside |
| gravity | a force that attracts all objects to one another |
| orbit | to follow a path around another object |
| release | escape or flow out |
| atmosphere | the air around a planet |
| craters | bowl-shaped holes on the surface of planets |
| surface | top of the ground |
| lava | hot melted rock |
| astronomers | scientists who study objects in space |
| spacecraft | machine that rockets to other planets |
| spew | spit out |
| collision | when two objects crash together |
| comparison | checking how two objects are the same or different |
| telescope | a scientific tool used to look at objects in space |
| asteroid | a large space rock |
| comet | a large ball of ice in space |
| solar system | the family of the sun, planets, asteroids, and comets |
| axis | the center point, or poles, around which planets spin |
| ellipse | the oval shape of the Earth's orbit |
