- A blue moon is a second full moon that occurs in the same calendar month. This happens because the lunar cycle of approximately 29.5 days is not exactly aligned with the Gregorian calendar months.
- There are usually 12 full moons in a year, with one in each month. A blue moon occurs when a year has 13 full moons instead, with two occurring in one month.
- Years with two blue moons are very rare, occurring once every few years, with one month (usually February) having no full moon.
- A blue moon is a second full moon that occurs in the same calendar month. This happens because the lunar cycle of approximately 29.5 days is not exactly aligned with the Gregorian calendar months.
- There are usually 12 full moons in a year, with one in each month. A blue moon occurs when a year has 13 full moons instead, with two occurring in one month.
- Years with two blue moons are very rare, occurring once every few years, with one month (usually February) having no full moon.