We have all heard the phrase once in a blue moon. Well what constitutes a blue moon has changed definition several times, but the most recent definition is the second full moon in any given month. Each moon in a month has a name, so the second moon in any given month is called the 'blue moon'. On average this occurs once every 2.7 years
Well we have been together for several years now, and have seen more than a few blue moons. So we started talking about a wedding date, near one of those blue moons, and began to speculate about could you have two blue moons in one year. Being math geeks, we figured out that you likely could and looked it up. Sure enough, the next double blue moon was March 31st, 2018.
So we decided back then that we would not get married once in a blue moon, but rather once in a double blue moon. The next one is in 2037, so we figured we better do it this time around.
Interestingly, the moon follows an approximate cycle of 19 years where the full moon will fall on about the same day. But given the small amount of mismatch, that full moon can fall either in January, or in February. If the second full moon of the season occurs in February, you can not have a double blue moon. The first two full moons MUST occur in January in order to have a double blue moon.
The third full moon of the year will always occur in March, but as it works out, the second blue moon of the year can fall in March, April, or May. This time around it will occur in March. It will also occur in March again in 2037, and amazingly there will also be another eclipse of the moon on January 31st, just like this year. The next one after that, however, won't be until April of 2094!
So yes, once in a blue moon seems like a long time, but once in a double blue moon is even longer.