Wow! Not until 2018? I guess that would mean more to me if I could remember when the last blue moon was...and I don't.

A couple of facts about the phenomenon of the blue moon, courtesy of

What is a Blue Moon?

There are in fact two definitions for a blue moon. According to the more recent definition, a blue moon is the second full moon in a calendar month. For a blue moon to occur, the first of the full moons must appear at or near the beginning of the month so that the second will fall within the same month (the average span between two moons is 29.5 days).

How Often Does a Blue Moon Occur?

Over the next 20 years there will be about 15 blue moons, with an almost equal number of both types of blue moons occurring. No blue moon of any kind will occur in the years 2011, 2014, and 2017.

The more recent phenomenon, where the blue moon is considered to be the second full moon in a calendar month, last occurred on August 31, 2012. Two full moons in one month may occur in any month out of the year except for February, which is shorter than the lunar cycle.

The other, older blue moon event, which happens when there are four full moons in a season, last occurred Aug. 21, 2013. Since this type of blue moon is reckoned according to the seasons, it can only occur in February, May, August, or November, about a month before the equinox or the solstice. 

Of course, the only blue moon you won't have to wait for until 2018 would be this one:

Noam Galai, Getty Images
Noam Galai, Getty Images