Lunar phases are the result of our seeing the illuminated half of the Moon at different angles. The Moon exhibits different phases as the relative positions of the Sun, Earth and Moon change, appearing as the Full moon when the Sun and Moon are on opposite sides of the Earth, and becoming invisible as the New Moon (also named Dark Moon) when they are on the same side.

The time between two Full Moons (or between successive occurrences of any two phases - for examples, First Quarter Moon to the next First quarter Moon) is about 29.53 days (or 29 days, 12 hours, 44 minutes); it is longer than the time it takes the Moon to orbit the Earth since the Earth-Moon system is orbiting the Sun. The phases are not created by the shadow of the Earth on the Moon (that would be a lunar eclipse); instead, they are a result of our seeing only part of the illuminated half of the Moon.

	New Moon The Moon's unilluminated side is facing the Earth.
	Waxing Crescent Moon The Moon appears to be partly but less than one-half illuminated by direct sunlight. The fraction of the Moon's disk that is illuminated is increasing.
	First Quarter Moon One-half of the Moon appears to be illuminated by direct sunlight. The fraction of the Moon's disk that is illuminated is increasing.
	Waxing Gibbous Moon The Moon appears to be more than one-half but not fully illuminated by direct sunlight. The fraction of the Moon's disk that is illuminated is increasing
	Full Moon The Moon's illuminated side is facing the Earth. The Moon appears to be completely illuminated by direct sunlight.
	Waning Gibbous The Moon appears to be more than one-half but not fully illuminated by direct sunlight. The fraction of the Moon's disk that is illuminated is decreasing.
	Last Quarter One-half of the Moon appears to be illuminated by direct sunlight. The fraction of the Moon's disk that is illuminated is decreasing.
	Waning Crescent The Moon appears to be partly but less than one-half illuminated by direct sunlight. The fraction of the Moon's disk that is illuminated is decreasing.