| A | B |
|---|
| astronomy | the study of the moon, stars, and other objects in space |
| rotation | the spinning motion of a planet on its axis |
| orbit | the path of an object as it revolves around another object in space |
| solstice | the two days of the year on which the sun reaches its greatest distance north or south of the equator |
| axis | an imaginary line that passes through a planet's center and north and south poles, and about which it rotates |
| revolution | the movement of an object around another object |
| equinox | the two days of the year on which neither hemisphere is tilted toward or away from the sun |
| force | a push or a pull exerted on an object |
| gravity | the attractive force between objects |
| mass | the amount of matter in an object |
| weight | the force of gravity on an object |
| inertia | the tendency of an object to resist a CHANGE in motion |
| law of universal gravitation | the scientific law that states that every object in the universe attracts every other object |
| Newton's first law of motion | the scientific law that 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 UNLESS ACTED UPON BY A FORCE |
| phase | one of the different apparent shapes of the moon as seen from Earth |
| solar eclipse | the blocking of sunlight to the Earth that occurs when the moon is directly between it and the sun |
| lunar eclipse | the blocking of sunlight to the moon when the Earth is directly between it and the sun |
| penumbra | the part of a shadow which surrounds the darkest part |
| unbra | the darkest part of a shadow |
| tide | the periodic rise and fall of the water in the ocean |
| spring tide | the tide with the greatest difference between consecutive high and low tides |
| neap tide | the tide with the least difference between consecutive low and high tides |
| eclipse | the partial or total blocking of one object in space by another |
| maria | dark, flat areas on the moon's surface formed by huge ancient lava flows |
| craters | large round pits caused by the impact of a meteoroid |
| meteoroid | a chunk of rock or dust in space |
