The Moon has phases because it orbits the Earth. As the Moon orbits the Earth, different parts of it are illuminated by the Sun. The phases of the Moon are the different amounts of the Moon’s illuminated surface that we can see from Earth.

The Moon’s phases repeat every 29.5 days. The four main phases of the Moon are:

• New Moon: The Moon is between the Sun and Earth, so we cannot see any of its illuminated surface.
• First Quarter: The Moon is halfway between the Sun and Earth, so half of its illuminated surface is visible.
• Full Moon: The Moon is on the opposite side of the Earth from the Sun, so all of its illuminated surface is visible.
• Last Quarter: The Moon is three-quarters of the way around the Earth from the Sun, so half of its illuminated surface is visible.

In between these main phases, there are also a number of intermediate phases, such as the waxing crescent and the waning gibbous.

The Moon’s phases are caused by the different angles at which the Sun’s light hits the Moon. When the Moon is between the Sun and Earth, the Sun’s light hits the side of the Moon that is facing away from us, so we cannot see any of its illuminated surface. This is called a new moon.

As the Moon orbits the Earth, the Sun’s light hits more and more of the Moon’s surface, until we can see half of it. This is called the first quarter.

The Moon continues to orbit the Earth, and eventually the Sun’s light hits all of its surface. This is called a full moon.

After the full moon, the Moon continues to orbit the Earth, and less and less of its surface is illuminated. This is called the waning gibbous.

Finally, the Moon is back to being between the Sun and Earth, and we cannot see any of its illuminated surface again. This is called a new moon.

The Moon’s phases have been observed and recorded by humans for centuries. They have been used to track the passage of time, to navigate the seas, and to predict lunar eclipses.