In geophysical terms, the moon is a planetary-mass object or satellite planet. Its mass is 1. 2% that of the earth, and its diameter is 3,474 km (2,159 mi), roughly one-quarter of earth's (about as wide as the … The moon is the earth's only natural satellite and the closest celestial object.

What is the moon made of, and how did it form? Learn about the moon's violent origins, how its phases shaped the earliest calendars, and how humans first explored earth's only natural satellite half a … We see the full moon when the sun is directly behind us, illuminating a full hemisphere of the moon when it is directly in front of us.