Why does the Moon have phases and what are they called?

Phases are caused by the amount of sunlight we see reflected by the moon. The phases take about 29 days to complete. From a new moon to a full moon, it is called waxing. Also from a full moon back to a new moon, it is called waining.

Waxing 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 increasing.

Note: half the Moon is illuminated by the Sun always. But depending on the position of the Moon and Sun in relation to us we might not see all the lit up part

Waxing 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 (and that we

see) is increasing.

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.

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.