| A | B |
|---|
| rotation | spinning of Earth on its axis, which occurs once every 24 hours, produces day and night, and causes the planets and stars to appear to rise and set |
| orbit | regular, curved path followed by Earth as it moves around the Sun |
| revolution | movement of Earth around the Sun, which takes a year to complete |
| eclipse | event that occurs when the Moon moves between the Sun and Earth (solar eclipse), or when Earth moves between the Sun and the Moon (lunar eclipse), and casts a shadow |
| solar system | system of nine planets and numerous other objects that orbit the Sun, all held in place by the Sun's gravity |
| astronomical unit | unit of measure that equals 150 million km, which is the mean distance from Earth to the Sun |
| comet | large body of frozen ice and rock that travels toward the center of the solar system; may originate in the Oort Cloud, and develops a bright, glowing tail as it approaches the Sun |
| meteorite | any space fragment that survives its plunge through the atmosphere and lands on Earth's surface |
| constellation | group of stars that forms a pattern in the sky and can be names after a real or imaginary animal, object, or person |
| supernova | very bright explosion of the outer part of a supergiant that takes place after its core collapses |
| galaxy | group of stars, gas, and dust held together by gravity |
| light-year | about 9.5 million km - the distance that light travels in one year - which is used to measure large distances between stars or galaxies |
