Many Moons

According to the calendar in our kitchen, there is a "blue moon" tonight.  ...or is there?...

If you're like most people you probably think a blue moon is the second full moon in a calendar month.  Or perhaps you don't, but you also don't particularly care.  It turns out, that like many things, blue moons have become sort of controversial.  It would seem that at some point in the 1800s someone writing in a Farmer's Almanac defined a blue moon as the 3rd full moon in a quarter of the year (quarter being defined by the solstices and equinoxes) in which there are 4 full moons.

Well, that's way too complicated.  Sometime later, in response to the question of what is a blue moon, someone cited that definition, but explained it as "the second full moon in a calendar month."  This is easier for people to get their heads around, so that definition has stuck.

To further complicate matters, depending on exactly when the moon is considered to be full, it is possible for a given cycle of the moon to be a blue moon in some timezones, but not in others.  It would seem that a moon gets to be officially blue, so long as it is blue in GMT.  Those Greenwich people get all the power when it comes to time.  Also, it would seem that with the exception of Jan/Feb, if one month has a blue moon in one timezone but not in another, the following month will have a blue moon.  In fact, this is the case with the current moons--the EDT's 5/31 full moon is a 6/1 full moon in GMT, so Greenwich didn't get a blue moon in May '07, but will in June.   But, it is not possible to ever have a blue moon in February b/c despite the popular belief that full moons occur 28 days apart (which would make a Feb. blue moon possible in a leap year), they actually occur on average 29.53 days apart.  So, if a 1/31 full moon from some timezones was a 2/1 full moon in others, there could not be a second full moon in the second TZ in Feb. 

And finally, just to add one more useless, random bit of information to our story, there is the phenomenon of 2 blue moons in a calendar year.  There is a name for this, but we forgot what it was and can't be bothered to go back to Google at this point, but we do remember this happens approximately every 19 years.

There.  Now don't you feel illuminated?