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What is a Blue Moon?
O
nce in a Blue Moon, on December 31, 2009
By: Slade Ogletree
I’ve always wondered what they were talking about when I was told “That’ll happen ‘once in a Blue moon”. Then I heard that we were going to see one here in Baja this month! A blue moon? Are you telling me that I’m going to see the Moon turn blue? I’ve seen eclipses and other phenomena, but this I have to see!!
It turns out that we may be disappointed with this one. While what we will experience on December 31st is a “Blue Moon”, there will be no light show. There will be no color change in the Moon’s appearance. The Moon we see will be just another full moon in May.
It’s not that a full moon rising over the Sea of Cortez isn’t an awesome sight. Trust me, it is. We usually have one full moon per month, right? Well we’ve already had our full moon in May. It happened several times in 2007. The second full moon to occur within a given month is called a Blue Moon.
Other factors such as forest fires, volcanic eruptions, and plain old air pollution can cause the moon to take on a bluish glow. This type of thing happened in 1991 when Mt Pinatubo blew its top in the Philippines. In the 1950’s forest fires in western Canada caused the same effect in some places, but these had nothing to do with the Blue Moons that we refer to here.
Mathematically, a blue moon occurs, on average, about every 32 months, but in 1999, three occurred in a two month span! The first record of the term was in 1824, but its official use began in 1932 with a reference in the Maine Farmer’s Almanac. They considered a blue moon as the fourth full moon in a three month season.
In 1946 Sky and Telescope magazine misinterpreted this to mean the second full moon in a given month. Several other sources continued to express the same misinterpretation through the 1980’s and that became the definition accepted today.
The full moon happens at exactly 12:13PM, Baja time. That’s 2:04 PM on the East Coast. Yes, that's right! The astronomical full moon actually will occur in the middle of the Baja day. Now you know the whole story.
Click here to see the US Navy Chart of Lunar Phases
This Month's Phases of the Moon
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Sep 1
Last Quarter
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Sep 8
New
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Sep 15
First Quarter
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Sep 23
Full
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