The different moon phases occur as a result of the position of the Moon in relation to the Earth and the Sun. As the Moon orbits the Earth, the amount of sunlight reflecting off its surface changes, leading to the varying appearances we see from Earth. The four primary moon phases are the new moon (when it’s not visible), the first quarter (half of the Moon is visible), the full moon (entire face is visible), and the third quarter (half of the Moon is visible). These phases cycle about every 29.5 days.