when does the blue moon appear

A Blue Moon appears either as the second full moon in a single calendar month (called a calendrical or monthly Blue Moon) or as the third full moon in a season that has four full moons (called a seasonal Blue Moon). Blue Moons are rare, occurring roughly every 2.5 to 3 years. The next calendrical (monthly) Blue Moon will happen on May 31, 2026, and the next seasonal Blue Moon will occur on May 20, 2027. Blue Moons are referred to as "blue" not because of their color, but due to their rarity and timing in the lunar calendar.