One of several vast, dark flat areas on the moon, Mercury, or Mars; smooth, dark areas on the moon
Light colored mountainous regions of the moon
The path followed by celestial bodies or artificial satellites as it revolves around another body due to the force of gravity
The force of attraction by which terrestrial bodies tend to fall toward the center of the earth
Define solar system:
the Sun together with all planets and other bodies that revolve around it
Either of the two times a year when the sun is at its greatest distance from the celestial equator: about June 21st, when the sun reaches its northernmost point on the celestial sphere or December 22, when it reaches its southernmost point.