What is a blue moon? A blue moon isn't blue at all. It's the name given to the second full moon in a calendar month. Two moons in one month don't happen all that often. Most years have 12 full moons, one appearing each month. But once every three years or so, an extra moon slips in. That's because our calendar is based on the amount of time it takes Earth to orbit the sun and not on the lunar month, which is 29½ days.
This definition of a blue moon is a modern one and it came about by mistake. Before 1946, the Farmer's Almanac said a blue moon was the third moon in a season that has four full moons. A writer for an astronomy magazine misunderstood the meaning and wrote that a blue moon was the second full moon in a month. This meaning stuck. In 1999, the error was discovered. But since more than 50 years had passed, most people continue to call the second moon in a month a blue moon.
Full Moon Names
Many cultures around the world gave names to each month's full moon. Here are the names from North America's Algonquin tribes. European settlers later adopted many of the names.
|MONTH||FULL MOON NAME|
Kwentologist Tells Your More!
The expression "once in a blue Moon" means something that happens rarely, just like two full moon in one month.