The Galileo spacecraft passed by Earth on its way to Jupiter. On December 16, 1992, it looked back to capture this remarkable view of the Moon in orbit about the Earth, taken from a distance of about 6.2 million kilometers (3.9 million miles). The Moon is in the foreground, moving from left to right, and the Sun is out of view to the far right. The brightly-colored Earth contrasts strongly with the Moon, which reflects only about one-third as much sunlight as Earth. Contrast and color have been computer-enhanced for both objects to improve visibility. (Credit: NASA and JPL)

The appearance of the Moon or the Earth depends on where we are and where the source of light is. From Earth, New Moon occurs when the Moon is nearly between the Earth and the Sun. Full Moon occurs when the Earth is between the Moon and the Sun. Compare the view of the Earth and Moon from space in the photograph to First Quarter in this drawing.

This remarkable sequence of images of the Moon (Copyright Antonio Cidadao, reproduced by permission) reveals not only the phases, but also other subtle phenomena. Notice that the Moon is larger when it is closer to Earth in its slightly eccentric orbit. When the Moon is closer it moves faster in its orbit, and reveals more of the western limb. When it is farther it is slower and we see more of the eastern limb. The Moon's rotation axis is tipped to the plane of its orbit. At times we see more of one pole, and then about two weeks later more of the other pole. The combined effects make the Moon appear to roll left and right, and up and down over the lunar month.