Blue Moon facts

My buddy Malcolm asked me about the "Blue Moon" thing. He asked me specifically, "How often do Blue Moons occur?" Hopefully, I clarified matters for him...

There is a "common" understanding that if you have 2 full Moons in a month, like what happened in December, that the 2nd full Moon is called a Blue Moon.

This is however an urban legend ultimately started due to a factual error in, ironically, a 1940 issue of Sky & Telescope magazine.

The Moon doesn't appear blue. Two full Moons in a month is not an extremely rare event. The lunar cycle is about 29.5 so that means by chance coincidence a double full Moon could fit within every month [including but very rarely] February. Statistically, it happens about every 3 years.

SkyNews magazine published a good myth-busting article.

So, in summary, there really is no such thing as an astronomical Blue Moon.