A full moon occurs roughly once every 29.5 days, which is the length of a complete lunar phase cycle (also called a synodic month). This means on average there is one full moon each month
. The full moon happens when the Earth is positioned between the Sun and the Moon, causing the Moon's near side to be fully illuminated as seen from Earth
. Because the lunar cycle is about 29.5 days and calendar months vary in length, occasionally a calendar month can have two full moons, known as a "blue moon"
. In summary:
- Full moon frequency: about every 29.5 days
- Usually one full moon per calendar month
- Sometimes two full moons in a month (blue moon)
- About 12 or 13 full moons per year
The exact timing of the full moon varies by time zone and location, and the full moon phase technically lasts only an instant, though it appears nearly full for about a day before and after
