For the phases to begin over again, the Moon, Earth, and Sun all have to line up in a row, whether you start a phase at a new moon or a full moon.
While one revolution of the Moon around Earth lines up the Moon and Earth again, the Sun is no longer in the same place.
This is because at the same time the Moon is orbiting Earth, the Earth–Moon system, the phrase used to describe Earth and its satellite as one unit, because they are relatively close to each other is orbiting the Sun.
The Earth–Moon system travels approximately 3.5 million miles (5.8 million km) around the Sun, at a speed of 66,600 miles (111,000 km) per hour.
It takes about two more days (orbit: 27.3 days; phase cycle: 29.5 days) for the Moon, Earth, and Sun to line up again.
It takes the Moon about 29.5 days to go from one new moon to the next.
The Moon orbits the Earth once every 27.3 days.
