| A | B |
|---|
| sphere | round 3D object whose surface at all points is the same distance from its center |
| axis | imaginary line around which an object spins |
| rotation | spining of object around axis |
| revolution | orbiting of one object around another, like Earth revolving around the sun. |
| ellipse | elongated closed curve; shape of planetary orbits |
| equinox | two times each year the sun is directly over equator and day and night are of equal length, start of spring and fall |
| solstice | two times each year that Earth's tilt makes the sun reach its greates angle north or south of the equator, marking summer and winter |
| moon phases | changes in appearance of the moon as it orbits Earth |
| new moon | moon phase when the side facing Earth is completely dark, because moon is between Earth and sun. |
| waxing | light area grows larger |
| first quarter | moon phase halfway between new moon and full moon, when half of the side facing Earth is lighted. |
| full moon | moon phase when the side facing Earth is completely lighted, because Earth is between sun and moon. |
| waning | the moon is getting smaller |
| third quarter | moon phase halfway between fuul and new, when half of the side facing Earth is lighted |
| solar eclipse | the passing of moon directly between Earth and sun, so moon blocks sunlight from reaching Earth. |
| lunar eclipse | passing of Earth between sun and moon so Earth blocks sunlight from reaching all or part of moon |
| maria | dark, flat regions of ancient lava on the moon; viewed from Eaarth they resemble oceans, |
| moon colony | permanent structure on the moon in which people could live and work |
