The moon, like Earth, is a sphere, and it is always half-illuminated by the sun. As the moon travels around Earth, we see more or less of the illuminated half. The moon's phases describe how much of the moon's disk is illuminated from our perspective. -- Space.com

More information about the phases of the moon can be found at TimeandDate.com. An interactive calendar is also available at Moon Phases Today

The phases of the moon are:

1. New Moon
2. Waxing Crescent
3. First Quarter
4. Waxing Gibbous
5. Full Moon
6. Waning Gibbous
7. Third Quarter
8. Waning Crescent

Using the slider below, scroll through the moon's cycle of phases. Images from PhasesMoon.com.