| A | B |
|---|
| ASTRONOMY | The study of the moon, stars, and the objects in space. |
| AXIS | An imaginary line that passes through Earth's center and the North and South poles, about which Earth rotates. |
| ROTATION | The spinning motion of a planet about its axis. |
| REVOLUTION | The movement of an object around another object. |
| ORBIT | The path of an object as it revolves around another object in space. |
| SOLSTICE | The two days of the year on which the noon sun is directly overhead at either 23.5° South or 23.5° North. |
| EQUINOX | The two days of the year on which neither hemisphere is tilted toward or away from the sun. |
| VERNAL EQUINOX | The day of the year that marks the beginning of spring in the Northern Hemisphere. |
| AUTUMNAL EQUINOX | The day of the year that marks the beginning of fall in the Northern Hemisphere. |
| PHASE | One of the different shapes of the moon as seen from Earth. |
| ECLIPSE | The partial or total blocking of one object by another. |
| SOLAR ECLIPSE | The blocking of sunlight to Earth that occurs when the moon is between the sun and Earth. |
| LUNAR ECLIPSE | The blocking of sunlight to the moon that occurs when Earth is directly between the sun and moon. |
| TIDE | The daily rise and fall of Earth's waters on shores. |
| GRAVITY | The attractive force between two objects; its magnitude depends on their masses and the distance between them. |
| SATELLITE | Any object that revolves around another object in space. |
| CRATER | A round pit on a planet's or moon's surface, created by a force of impact. |
| SMALL SOLAR SYSTEM BODIES | Solar system celestial bodies that don't fall in the planet, dwarf planet, moon, or meteroid category. |
| METEOROID | small rocky or iron body in space |
| METEOR | burning rocky object falling through the atmosphere; often no larger than a grain of rice |
| METEORITE | remains of a meteor that hits the ground |
| PLANET | orbits the sun, enough mass to have enough gravity to be round, clears its neighborhood of other similar objects |
| DWARF PLANET | orbits the sun, has enough mass to have enough gravity to be round |
| STAR | large gaseous (plasma) object that generates its own heat and light through fusion |
| MOON | generally a rocky body that orbits a plant, dwarf planet, or asteroid |
| GALAXY | a single collection of billions of stars and star systems |
| ASTEROID | large rocky object in orbit around the sun; most are between Mars and Jupiter |
| COMET | rocky and icy object that orbits the sun; highly eccentric orbit; appears to grow a tail when close to the sun |
| AU - Astronomical Unit | distance between Earth and the Sun; used to more easily compare and measure the distances from the sun for each planet |
| LIGHT YEAR | the DISTANCE light can travel in a year - (at 150,000,000 km/sec - the speed of light) |
