| A | B |
|---|
| planetary system | a system of planets revolving around a star |
| asteroid | a chunk of rock and metal, smaller than a planet and larger than a meteroid, that orbits the sun |
| meteoroid | a chunk of material smaller than an asteroid that orbits the sun |
| comet | a ball of ice, rock, and frozen ashes that orbits the sun |
| astronomical unit | a measurement equal to the distance between Earth and the sun, a distance of about 150 million km |
| rotation | the turning of an object on an axis |
| orbit | the path an object follows as it revolves around another object |
| ellipse | an oval shaped path |
| season | a period of the year with a certain level of temperature and type of weather |
| axial tilt | the angle that a planet's axis is tilted from vertical |
| phase | a stage in the changing shape that the moon seems to have when it is viewed from Earth |
| first quarter | the waxing phase of the moon viewed from Earth where half the moon's lit side is visible |
| third quarter | the waning phase of the moon viewed from Earth where half of the moon's lit side is visible |
