| A | B |
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| sphere | a round, three-dimensional object whose surface at all points is the same distnce from its center; Earth is a sphere that is slightly flattened at its poles |
| axis | an imaginary line around which an object spins for example, Earth spins around its axis |
| rotation | the spinning of an object around its axis causes day and night to occur on Earth |
| revolution | the orbiting of one object around another, like Earth's yearly orbit around the sun |
| ellipse | an elongated, closed curve; the shape of Earth's orbit |
| equinox | the two times each year that the sun is directly above Earth's equator and the day and night are of equal length all over the world, the start of spring and fall |
| solstice | the two times each year that Earth's tilt makes the sun reach its greatest angle north or south of the equator, marking the start of summer or winter |
| moon phase | the change in appearance of the moon as it orbits Earth every 29 1/2 days, depending on the relative postions of the moon, Earth, and the sun; for example, full moon and new moon |
| new moon | the moon phase when the side facing Earth is completely dark and cannot be seen because the moon is between Earth and the sun |
| waxing | describes the moon shortly after a new moon, as its visible lighted area grows larger during the lunar cycle |
| first quarter | the moon phase halfway between new moon and full moon, when half of the side facing Earth is lighted |
| full moon | the moon phase when the side facing Earth is completely lighted because Earth is between the sun and the moon |
| waning | describes the moon following a full moon, as its visible lighted area grows smaller during the lunar cycle |
| third quarter | the moon phase halfway between full moon nad new moon, when half of the side facing Earth is lighted |
| solar eclipse | an eclipse that occurs when the moon passes directly between Earth and the sun, so that the moon casts a shadow on part of Earth and blocks sunlight from reaching Earth |
| lunar eclips | an eclipse that occurs when Earth passes between the sun and moon, and Earth's shadow falls on the moon, preventing sunlight from reaching all or part of the moon |
| maria | dark, flat regions of ancient lava on the moon; viewed from Earth, they resemble oceans, the Latin word for which is maria |
| mascon | the concentration of mass on the moon located under an impact basin |
