Blue Moons

Well, tonight is the night of the Blue Moon. If you live in an area with a lot of cloud cover, do not fret, the moon is not really blue tonight. It is not even made of blue cheese as I had been told as a child. I also remember hearing the phrase, "Once in a Blue Moon". That phrase was intended to mean that the particular event happens rarely.

There are actually two definitions of Blue Moons. The first definition, which is the one I was aware of, was a second full moon in a single calendar month. Since the lunar cycle is usually 28 days, at some point you may encounter two full moons in the same month, or 13 full moons in a calendar year. Since there is only a few days difference between our calendar months and the lunar months, the occurrence of a double full moon in one month occurs about once every 2-3 years.

There are even very occasions where we have two full moons in one month, and then no full moons in the following month. That occurred in 1999 where there were two full moons in January, none in February (a traditionally short month, and then two full moons in March. The next time we can see a double Blue Moon will be in 2018, so now you have something to look forward to...

The second definition comes from an old Farmers Almanac definition. In the Farmers Almanac, a Blue Moon occurs when an extra full moon occurs in a season. So for November 21, 2010 we will have already had our 3rd full moon, with the 4th full moon occurring in December. Generally, a season only has 3 full moons in it.

Based on both definitions, November 21, 2010 is a Blue Moon, but this agreement does not always occur. Some people prefer to use the definition of the third full moon of four in a season is the more accurate definition of a Blue Moon because it appears to be the older definition. Whichever definition you personally prefer, tonight is truly a Blue Moon.

If you have clear skies tonight, enjoy the full, Blue Moon. Otherwise, you can look to the sky, use your imagination and enjoy the Blue Moon that is there, but you can't see it...

Until tomorrow...