Mom used to say “once in a blue moon.”
I would giggle thinking that was a funny saying, the moon could be white or orange or even yellow, but I had never seen a blue moon, or had I?
After looking up the definition, I decided that I had seen many blue moons, but had just never realized it.
According to earthsky.org, a blue moon is, according to modern folklore, the second full moon of a calendar month.
Wikipedia tells me that the Farmers’ Almanac defines blue moon as the third full moon in a season of four full moons.
A blue moon is said to occur every 2 1/2 to 3 years. That would also give me reason to believe that the saying “once in a blue moon,” would simply mean seldom. So if I asked how often do you ... (whatever it might be) and you reply “oh, once in a blue moon,” I would know that it is not very often.
My entire life I never knew the origin of blue moon, or just how long it was.
But since I’ve seen some news reports saying that there is a blue moon tonight, I wanted to find out just what that is. Would I actually see a moon, full and bright in the sky, and blue?
I now know that even though it is rare, seeing a blue colored moon is possible if the unusual sky conditions and certain sized particles of dust or smoke are just right. Spaceweather.com says that sometimes the moon really does turn blue, usually after volcanic eruptions or major forest fires. It says that volcanoes and wildfires fill the air with ash and dust. If the airborne particles are just the right size, they act like a color filter and give the moon a blue tinge. It says that clouds of water droplets, ice crystals or fine-grained sand can also do the same thing.
Even though the color blue is not predictable, it is still referred to as “blue.” Or, an easier way to see a blue moon, would be to hold a blue colored plastic between your eyes and the full, bright moon, then it will of course look as though it is blue.
According to the blue moon between 2009 and 2016 on Wikipedia, the next seasonal blue moon is said to be Aug. 21, 2013 and the next calendar blue moon, besides tonight, is said to be July 31, 2015.
So if you want to know when I am going to do something and I say “once in a blue moon,” know that it will most likely be within the next 2 1/2 or 3 years.
It was actually a mistake by an amateur astronomer in Sky & Telescope magazine in 1946 that led to our current definition of “blue moon” as the unusual second full moon in a month.
The term “blue moon” goes back hundreds of years, but it had a different meaning then of “impossible” or “absurd.” The term later morphed into a reference for something uncommon or that rarely occurred.
There are normally three full moons in each of the four seasons, for a total of 12 per year. In the early 1930s, the Maine Farmers’ Almanac (unrelated to the Old Farmer’s) named the third full moon in a season that had an extra fourth full moon a blue moon. It’s unclear where the “blue” part came from, but it’s possible it refers to that earlier meaning – an event that rarely happens.
Then, in the March 1946 issue of Sky & Telescope magazine, American amateur astronomer James Hugh Pruett wrote an article titled “Once in a Blue Moon.” He either misread the Maine almanac’s definition or interpreted the meaning of “blue moon” differently, calling it the second full moon in a month. Sky and Telescope later adopted Pruett’s definition.
Blue moons between 2009 and 2016
The following blue moons occur between 2009 and 2016. These dates use UTC as the timezone; exact dates vary with different timezones.
Using the Farmers’ Almanac definition of blue moon (meaning the third full moon in a season of four full moons), blue moons occur
• Nov. 21, 2010
• Aug. 21, 2013
• May 21, 2016
It seems that The Farmers Almanac, even though it describes the Sky & Telescope ‘invention’ of the new definition, is now using the new definition of blue moon on its calendar, therefore indicating that the blue moon is Aug. 31, 2012 instead of August 21, 2013.
Unlike the astronomical seasonal definition, these dates are dependent on the Gregorian calendar and time zones.
Two full moons in one month:
• 2009: Dec. 2, Dec. 31 (partial lunar eclipse visible in some parts of the world), only in time zones west of UTC+05.
• 2010: Jan. 1 (partial lunar eclipse), Jan. 30, only in time zones east of UTC+04:30.
• 2010: March 1, March 30, only in time zones east of UTC+07.
• 2012: Aug. 2, Aug. 31, only in time zones west of UTC+08.
• 2015: July 2, July 31
The next time New Year’s Eve falls on a Blue Moon (as occurred on Dec. 31, 2009) is after one Metonic cycle, in 2028. At that time there will be a total lunar eclipse.
Once in a blue moon
Mom used to say “once in a blue moon.”