What is the Moon?

The Moon does not have any light of its own, but shines because sunlight is reflected off it. On half of the Moon is always lit by the Sun and the other half is in the darkness. In the same way, Earth always has one half in daylight and one in the darkness of night. As the Moon travels around us, we see differing amount of the sunlit half. In this way, the moon appears to change shape.

These different shapes are the phases of the Moon. A complete cycle of the Moon's phase takes 29.5 days. It goes from new moon, when the side facing us is completely dark, to full moon, when this side is completely lit, and back to new moon, to start all over again. It is possible to see some of the Moon's surface features by looking at it with the naked eye. The lighter areas are older, higher land, and the darker ones, younger, lower and flatter land. Binoculars and telescopes will reveal that the whole of the surface is covered in impact craters. Most of these were formed when the Moon was bombarded by space rock between three to four billion years ago. Over the next billion years lave seeped through cracks in the Moon's crust and flooded the largest craters to form maria. These are the dark regions visible with the naked eye. The first astronomers to observe them called them seas because that is what they thought they were.