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A full moon above clouds
How Rare Are Blue Moons?
History - Science
A blue moon denotes a second full moon that occurs in one month. While these moons aren’t actually blue, they can happen every two to three years and are considered rare.
The most recent blue moon was on August 30, 2023. Before that, the most recent one was on August 22, 2021, and the one before that was on Halloween 2020, the first in 19 years.
A full moon typically occurs once a month. However, a second one can occur because of a lapse between calendar months and lunar months.
Blue moons occur as a result of how humans arrange time. The Gregorian calendar, which is commonly used today, is based on the sun, not the moon.
The seasons mostly align with the lunar cycle, but sometimes they don’t. Simply put, blue moons are merely a result of the Gregorian calendar and are not special otherwise.