'Once in a blue moon' this happens. Two full moons in the same calendar month. Most years we have 12 full moons but this year we'll have 13. Now the moon isn't actually blue (although it can happen) it looked like any other full moon.

Why is it called a blue moon if it's not blue? The term blue moon first appeared in writing in the 16th century  from Cardinal Wolsey" — Henry VIII's notorious adviser. He wrote about his intellectual enemies who 'would have you believe the moon is blue' according to Phillip Hiscock, a professor at Memorial University in Newfoundland who has traced the meaning of the phrase through the centuries.

Later it turned into a metaphor for absurdity or impossibility. Then in the 1700s, the phrase had acquired a related meaning: never. "It sort of slipped sideways from impossibility to a temporal notion of impossible in time," Hiscock said. In the 19th century it turned up as street slang in London meaning 'a long time.'

This meaning  ‘not very often,’ or ‘very rarely,’ has become the commonly accepted one. It was further fixed into modern use when it was broadcast on the popular radio program StarDate on January 31, 1980.  The author of that program was Deborah Byrd, who also writes for the radio program Earth & Sky, gives her perspective on this modern contribution to lunar-folklore.

The last time this happened was August 2012. If you missed the blue moon this month you'll have to wait until January 2018 to see the next one. Or take a look at my these photos.