The moon does not actually shine but is illuminated by light from the sun. As the moon continues in its orbit, the amount of light reaching the surface of the moon varies according to where it is in relation to the sun. It is these changes that create the phases of the moon.
The moon appears in eight different phases, from a new moon to a full moon and back again. While the Earth rotates and orbits the sun, the moon is also rotating on its own axis and always has the same side facing towards Earth. The far side of the moon is never visible from any point on Earth.
New moon
The narrow crescent shape of a new moon occurs when the moon and the sun are on the same side and only a minimum amount of light from the sun is reflected by the moon. The amount of light illuminating the moon will slowly start to increase as the lunar orbit moves it through the next four phases.
Waxing crescent
As the Earth continues in its orbit of the sun and the moon continue in its orbit around the Earth, more light from the sun begins to light up the moon. This is known as waxing.
First quarter
The light from the sun reaches half of the moon’s surface when it is in its first quarter.
Waxing gibbous
The moon becomes gibbous, meaning that it is a phase between the first quarter and the full moon when more than half the moon is illuminated.
Full moon
The moon appears as a complete circle of light when it’s opposite the sun. The moon appears larger and brighter when its perigee orbit brings it closest to Earth and it becomes a super moon.
Waning gibbous moon
The next phase after the full moon is known as a gibbous moon, which means it is less than full, but more than half of the moon is illuminated.
Last quarter moon
When only half the moon is illuminated, this it is due to the line between the Earth and the sun being at right-angles to the moon. This phase is also known as the third quarter.
Waning crescent
This occurs when light from the sun is restricted to lighting up only a narrow crescent of the surface of the moon. It is also known as an old moon. This time the crescent appears on the opposite side of the moon from a Waxing Crescent, and the moon continues to wane until it becomes another new moon.
The pattern repeats each lunar month, which is the time it takes for the moon to complete its orbit around the Earth.
According to Dr Richard W Pogge, in his lecture on The Phases of the Moon, it is not possible to view all the phases of the moon as they happen. A crescent moon will never be visible at midnight and the last quarter cannot be seen during sunset. In the daytime, when light from the sun is strong, a full moon will not be visible in the sky.
As stated in the h2gh entry on Lunar Phases, the moon will appear to be upside down to someone who travels from one hemisphere to the other.
The other difference in viewing the moon from different parts of the Earth relates to where the moon appears in the sky in the northern and southern hemispheres, depending on whether it is summer or winter.
Each phase of the moon will be the same in all parts of the Earth. The moon will only be visible at certain times, as our planet rotates, rising into the sky and sinking from view once every twenty-four hours.
The moon has phases because of how it is placed in the solar system in relation to the Earth and the sun. Viewed from the Earth, the moon changes its appearance depending on how much light from the sun is reflected by the surface of the moon.
