| A | B |
|---|
| satellite | A body that orbits a planet. |
| comet | A cold mixture of dust and ice that gives up a long trail of light as it approaches the sun. |
| planet | An object that orbits the sun, is large enough to have become rounded by its own gravity, and has cleared the area of its orbit. |
| star | A giant ball of hot gas, mainly composed of hydrogen and helium. |
| meteor | A steak of light produced when a small object burns up entering Earth's atmosphere. |
| constellation | A pattern or group of stars that people imagined to represent a figure, animal, or object. |
| axis | The imaginary line that passes through Earth's center and the North and South poles. |
| calendar | A system of organizing time that defines the beginning, length, and divisions of a year. |
| rotation | The spinning of the Earth of its axis. |
| solstice | The day when the sun either appears farthest north or south of the equator. |
| revolution | The movement of one object around another. |
| equinox | Means "equal night." Halfway between the solstices when neither hemispher is tilted toward the sun. |
| orbit | Earth's path around the sun. |
| force | A push or pull. |
| mass | The amount of matter in an object. |
| gravity | The force in our universe that attracts all object toward each other. |
| weight | The measure of the force of gravity on an object. |
| law of the universal gravitation | This law states that every object in the universe attracts every other object. |
| inertia | The tendence of an object to resist a change in motion. |
| Newton's first law of motion | This law states that an object at rest will stay at rest and an object in motion will stay in motion with a constant speed and direction unles acted on by a force. |
| phase | The different shapes of the moon that we see from Earth. |
| eclipse | When an object in psace somes between the sun and a third object, it casts a shadow on that object. |
| solar eclipse | This occurs when the moon passes directly between Earth and the sun, blocking sunlight from the Earth. |
| umbra | The very darkest part of the moon's shadow. |
| penumbra | Th moon casts another part of its shadown that is less dark and is the larger part of the shadow. |
| lunar eclipse | This occurs at a full moon when Earth is directly between the moon and the sun. |
| tide | The rise and fall of ocean water that occurs every 12.5 hours or so. |
| spring tide | Means "to jump." When the sun, the moon, and Earth are nearly in a line during a new moon causing the combined gravitational force to produce a tide with the greatest difference between consecutive low and hight tides. |
| neap tide | A tide with the least difference between consecutive low and high tides. |
| maria | Dark, flat areas on the surface of the moon. |
| crater | Large round pits on the surface of the moon. |
| meteoroid | Chunks of rock or dust from space that impact the surface of a planet or moon. |
