asteroid

• a small rocky object in space

axis

• a line through the center of a sphere or planet

comet

• an object in space that is made mostly of ice and dust and may appear to have a “tail”

eclipse

• the hiding of a planet or the moon by the shadow of another; a way in which planets, moons, and stars (such as the Sun) line up so that one creates a shadow hiding the view of another

ecliptic

• the plane of Earth's orbit around the Sun

elliptical

• shaped in an oval

gibbous

• showing more than half, but not the whole, especially of the moon

gravity

• the pull of the earth on an object; a mutual physical force attracting two bodies, such as planets; the force of attraction between two or more objects, the strength of which is determined by mass and distance

orbit

• a path that circles around something, especially a body in space such as a planet

planet

• a large body in space that rotates around a star and does not give off light itself, but reflects light from the star

rotation

• a spin; a turn around something

satellite

• an object that goes around a larger body; an object that goes around a planet and is held in orbit by gravity

Satellites can be natural, like the moon (left), or man-made like this weather satellite (right).

tide

• the rising and falling levels of the ocean that happens twice each day

wane

• to shrink or become smaller

wax

• to grow and become larger