Tonight’s Moon is a True Blue Moon…Really!!
A Blue Moon as many of us know it…is when there are two full moons in a month. These are not true “Blue Moons”. The definition has gotten obscured over the years. Back in the 1930’s (August 21st 1937 to be exact) we had a fourth full Moon during the summer season. Seasonal Moons were given the designation of Early (in this case summer)…Mid summer and the late summer moon. So when it was observed that another Moon in a season couldn’t be called the late summer moon “again” the term Blue moon was assigned to the third full moon leaving the late full moon for the last occurrence in a season. Tonight’s Blue Moon will be the third full moon in the Fall Season. Not the Second full moon this month.
So where did the urban myth go astray…and where did the widely accepted two full moons in a month become the Blue Moon? Seven times in 19 years there were – and still are – 13 full moons in a year. This gives 11 months with one full moon each and one with two. This second in a month, has been wrongly interpreted and called a Blue Moon.
The original Maine Farmers' Almanac rule had been all but forgotten. Now, let's come back to tonight’s full moon. Under the old Almanac rule, this would technically be a blue moon. In the autumn season of 2010, there are four full moons: 
- Sept. 23
- Oct. 22
- Nov. 21
- Dec. 21
"But wait," you might say. "Dec. 21 is the first day of winter."
And you would be correct, but only if you live north of the equator in the Northern Hemisphere. South of the equator it's the first day of summer.
In 2010, the solstice comes at 6:38 p.m. EST.
But the moon turns full at 3:13 a.m. EST. That's 15 hours and 25 minutes before the solstice occurs. So the Dec. 21 full moon occurs during the waning hours of fall and qualifies as the fourth full moon of the season.
To add one further complication to the Blue Moon Theory…An extra full moon in a month…four full moons in a Season or how about this thought? After forest fires or volcanic eruptions, the moon can appear to take on a bluish or even lavender hue. Soot and ash particles, deposited high in the Earth’s Atmosphere, can sometimes make the moon appear bluish.
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