Introduction

The revolution of the Moon around the Earth makes the Moon appear as if it is changing shape in the sky.  This is caused by the different angles from which we see the bright part of the Moon's surface.  These are called "phases" of the Moon.  Of course, the Moon doesn't generate any light itself; it just reflects the light of the Sun.  The Moon passes through four major shapes during a cycle that repeats itself every 29.5 days.  You can see the phases drawn in the image below. The phases we see result from the angle the Moon makes with the Sun as viewed from Earth. The phases always follow one another in the same order. 

Below are pictures of the four major shapes and a description of each.

	New Moon: The lighted side of the Moon faces away from the Earth.  This means that the Sun, Earth, and Moon are almost in a straight line, with the Moon in between the Sun and the Earth.  The Moon that we see looks very dark. The Moon's unilluminated side is facing the Earth. The Moon is not visible (except during a solar eclipse).
	First Quarter: The right half of the Moon appears lighted and the left side of the Moon appears dark. One-half of the Moon appears to be illuminated by direct sunlight. The fraction of the Moon's disk that is illuminated is increasing. During the time between the New Moon and the First Quarter Moon, the part of the Moon that appears lighted gets larger and larger every day, and will continue to grow until the Full Moon.
	Full Moon: The lighted side of the Moon faces the Earth.  This means that the Earth, Sun, and Moon are nearly in a straight line, with the Earth in the middle.  The Moon that we see is very bright from the sunlight reflecting off it. The Moon's illuminated side is facing the Earth. The Moon appears to be completely illuminated by direct sunlight.
	Last Quarter: Sometimes called Third Quarter.  The left half of the Moon appears lighted, and the right side of the Moon appears dark.  During the time between the Full Moon and the Last Quarter Moon, the part of the Moon that appears lighted gets smaller and smaller every day. It will continue to shrink until the New Moon, when the cycle starts all over again.
There are also four other phases of the Moon sometimes used.  They are as follows:
	This is known as a Waxing Crescent Moon.  This Moon can be seen after the New Moon, but before the First Quarter Moon.  The crescent will grow larger and larger every day, until the Moon looks like the First Quarter 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.
	This Moon is known as a Waxing Gibbous Moon.  This Moon can be seen after the First Quarter Moon, but before the Full Moon.  The amount of the Moon that we can see will grow larger and larger every day.  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. ("Waxing" means increasing, or growing larger.)
	This Moon is called a Waning Gibbous Moon.  This Moon can be seen after the Full Moon, but before the Last Quarter Moon.  The amount of the Moon that we can see will grow smaller and smaller every day. ("Waning" means decreasing, or growing smaller.)
	This Moon is called the Waning Crescent Moon.  This Moon can be seen after the Last Quarter Moon and before the New 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 decreasing. The crescent will grow smaller and smaller every day, until the Moon looks like the New Moon.