A Peterson Field Guide to Stars and Planets

Excerpts: The moon is often the most prominent object in the nighttime sky. Themoon is somewhat more than one-quarter the diameter of the earth.This makes it the largest substantial satellite (moon) in the solarsystem in comparison to its parent planet. (Three moons of Jupiterand one each of Neptune and Saturn are physically larger than ourmoon; Pluto's small moon Charon is nearly half Pluto's size.)The moon orbits the earth every 271?3 days withrespect to the stars. But during that time, the earth and moon havemoved as a system about 1?12 of the way in their yearly orbit aroundthe sun. So if the moon at a certain point in its orbit is directlybetween the earth and the sun, 271?3 days later it has not quitereturned to that point directly between the earth and the sun. Themoon must orbit the earth a bit farther to get back to the same placewith respect to the line between the earth and the sun. The moonreaches this point in a couple of days, making the synodic period ofthe moon equal t