What is a Blue Moon? When is the next Blue Moon? There’s some confusion about its meaning. Here’s the scoop.
Why is it Called the Blue Moon?
We got a lot of letters about this. Some folks imagine that it actually appears blue. Others assume it’s a term that originated with Native American folklore. Neither is true.
Also, Blue Moon is not an astronomical term. This term only started in the 1940’s as a result of a mistake in an astronomy magazine. But it slowly went viral in the media.
Nowadays, Blue Moon has popularly come to mean “the second full Moon in the same calendar month.”
The notion has no venerable pedigree among Native Americans, ancient cultures, or anything in the actual sky. So OK, we’ll play along and call it a Blue Moon. Just so you know, it’s a new idea.
How Often Do We See a Blue Moon?
Most months have one Full Moon, not two. See the Almanac Moon Phase Calendar.
However, since the Moon’s period of phases is 29 ½ days, while months usually have 30 or 31 days, it’s obvious that if a full Moon lands on the first day of any month except February it will repeat again at the end.
Ever heard the expression, “Once in a Blue Moon?” Turns out, Blue Moons happen every 30 months on average. Two and a half years.
When is the Next Blue Moon?
As of this writing, the next Blue Moon (second full moon in one calendar month) is January 31, 2018.
Not so very rare. Once in a Blue Moon? Stick around!
Are you a Moon lover? Use our Moonrise and Moonset calculator to find out when you can see the Moon!