Blue Moon graces skies on August 31, 2012

A bright "blue moon" graces skies Friday August 31 tagged as the last one until July 2015. The last time sky-watchers were treated to a blue moon was New Year's Eve 2009.

Blue Moon graces sky August 2012

If the skies are clear, revelers will get an eyeful of the second full moon of the month—commonly called a blue moon. A blue moon isn't actually blue—as commonly defined, the name reflects the relative rarity of two full moons in a month and is linked to the saying "once in a blue moon."

"There is nothing scientific about it, and it has no astronomical significance," Mark Hammergren, a staff astronomer at the Adler Planetarium in Chicago, Illinois, said in 2009.

"But I believe it does give us some insight into history and makes us think of how our calendar system has derived from motions of objects in the sky.", he added.

'True' Blue Moon

Before the editorial error, the term "blue moon" more often referred to the rare instances when the moon actually seemed to turn blue, as can happen under certain atmospheric conditions.
"After a forest fire or volcanic eruption, there may be enough particulate matter in the air so that the moon can take on a bluish tinge," Hammergren said.

For instance, a "true" blue moon occurred in 1950 after a large forest fire in Canada blew smoke across most of the Northern Hemisphere.

Another appeared in 1980 after the last major eruption of Mount St. Helens, which sent tons of ash into the upper atmosphere.

"There are plenty of wildfires burning in the hot, dry U.S.A. this month," according to NASA Science News. "If any of them produce smoke with an extra dose of micron-sized particles, the full moon might really turn blue."

Details courtesy of National Geographic

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