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What is a ‘blue moon’?

Richard Brooks, Bristol

A lunar month is slightly shorter than a calendar month, so every two to three years, there is an extra lunar cycle above the usual 12. This additional moon is called the ‘blue moon’ and is the origin of the phrase meaning a rare event. And, the Moon can be literally blue when pollution or volcanic eruptions block red light in the atmosphere, giving our satellite a blueish hue.

Comments: 1

Blue Moon

Sat, 2010-01-02 13:44
Guest

http://www.skyandtelescope.com/observing/objects/moon/3304131.html?showAll=y&c=y
The above link explains in great detail the controversial definition of a "blue moon" and in particular why the assertion here that full-moon number 13 is the "blue moon" is incorrect ... a blue moon is actually the moon which restores the naming conventions linking full-moons to a particular season and as such might be considered to be a "leap full-moon"

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