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Blue moon shines around the world

Bill Ingalls / NASA

NASA photographer Bill Ingalls, who was in Cincinnati to take pictures during Apollo 11 moonwalker Neil Armstrong's family memorial ceremony on Aug. 31, snapped this picture of the "blue moon" hanging over the Queen City's skyline. See some of Ingalls' pictures from the memorial ceremony.

Tonight's blue moon may not be as rare as it sounds, but it's still special — as is every glorious full moon, whichever color you use to describe it.

Actually, the term "blue moon" is something of a misnomer. There's no reason for the full moon to be any bluer than usual (though it's certainly possible for the moon to take on a blue tinge). Instead, it has to do with the extra occurrence of a full moon in a given calendar cycle.

Various cultures have used different terms to describe that extra lunar cycle — Adhik Maas for Hindus, or an extra month of Adar for the Jewish calendar. The Maine Farmers' Almanac used the term "blue moon" to describe an extra moon in a particular quarter of the year.

Then, in 1946, an amateur astronomer named James Hugh Pruett wrote about the phenomenon for Sky & Telescope magazine, in the context of the old saying that a rare occurrence happened only "once in a blue moon."

Only problem was, he got it wrong.

Pruett described the blue-moon phenomenon as the second full moon in a calendar month. Sky & Telescope stuck with that, and the definition has been used (and hotly debated) ever since. If you go along with the definition, then tonight's full moon is blue due to the fact that it follows a full moon on the night of Aug. 1.

There's another long-debated issue surrounding blue moons: You could argue that they happen way too often to be considered as rare as a "blue moon" in the proverbial sense. The interplay of the lunar and solar calendars dictates that a blue moon should occur, on average, every 2.7 years.

Astrophysicist Neil deGrasse Tyson summed up the issue a couple of days ago in a Twitter update: "A month's second full moon is the blue moon. Not rare. More frequent than presidential elections, yet nobody calls them rare."

Technically speaking, the moon is already a few hours past its full phase — but it's still well worth taking note of, and not just because it's the last blue moon until July 31, 2015. It provides a fitting opportunity to pay tribute to history's first moonwalker, Neil Armstrong, who passed away last weekend. In fact, Armstrong's family is urging you to look at the moon in Neil's honor.

"The next time you walk outside on a clear night and see the moon smiling down at you, think of Neil Armstrong and give him a wink," the family said.

Photographers around the world have already been getting great moon shots. Here's a sampling of the "blue moon" views:

Biswaranjan Rout / AP

A boy rides his bicycle over a stretch of sand on the outskirts of the eastern Indian city of Bhubaneswar as the "blue moon" shines above in Aug. 31.

Muhammad Hamed / Reuters

A full moon shines over Amman, the capital of Jordan, on Aug. 31.

Robert Atanasovski / AFP - Getty Images

A full moon is seen behind tree branches in the Macedonian city of Skopje on Aug. 31. According to NASA, this is the second time in August that a full moon has been seen. The first was on the night of Aug. 1-2. This phenomenon is referred to as a "blue moon."

Vesa Vauhkonen

Vesa Vauhkonen created this multiple-exposure photographic view of the moon rising over Rautalampi, Finland, on Aug. 30.

Daisuke Tomiyasu

The clouds over Kobe, Japan, take on a fittingly blue hue in this picture taken by Daisuke Tomiyasu on Aug. 31.

Louisa Gouliamaki / AFP - Getty Images

Greeks and tourists gather at the Roman Agora in Athens, which is open all night as part of a full-moon celebration on Aug. 31. A number of archaeological sites and museums around Greece opened at night, with events and concerts celebrating the second full moon of August, known as a "blue moon."

Louisa Gouliamaki / AFP - Getty Images

A picture taken on Aug. 31 shows the full moon above the ancient Acropolis hill in Athens.

Inge Harsten

Inge Harsten, who lives in Fredrikstad, Norway, used a filter to add an appropriate color to this picture of the "blue moon."

Petros Karadjias / AP

The full moon rises over the sea at Konnos beach near Ayia Napa and Protaras resort in the southeast of the island of Cyprus on Aug. 31.

For still more blue-moon pictures, check out SpaceWeather.com's photo gallery and NASA's Flickr site for blue-moon imagery. If you snap a great picture of the moon tonight, please consider sharing it with us. Use our FirstPerson upload tool to send us your moon shot, and we'll pass along a sampling of the photos we receive.

Where in the Cosmos
Vesa Vauhkonen's moonrise montage served as the subject of this week's "Where in the Cosmos" photo quiz on the Cosmic Log Facebook page. It took a while this time, but John Culp and Brian Svacina eventually guessed that the photo was taken in Finland. To reward their geographical smarts (or was it just plain luck?), I'm sending them pairs of 3-D glasses, provided courtesy of Microsoft Research's WorldWide Telescope project. Those red-blue glasses will add an extra dimension to moon pictures like this one. Got 3-D? Click the "like" button for the Cosmic Log Facebook page and get ready for next Friday's quiz.

Update for 8:20 p.m. ET: The Phrase Finder delves deeply into the origins of the phrase "blue moon," meaning a rare event, and appears to have come up with a sensible explanation. In 16th-century England, the expression was apparently used to describe an impossible event, like pigs flying. The phrase pops up in a sarcastic context in a 1528 work by William Barlow, Bishop of Chichester, titled "Treatyse of the Buryall of the Masse": "Yf they saye the mone is belewe, we must beleve that it is true."

It took centuries longer for the phrase to describe something that hasn't happened in quite a while. The Phrase Finder cites this quote in Pierce Egan's "Real Life in London" (1821): "How's Harry and Ben? — haven't seen you this blue moon." Meanwhile, the Maine Farmers' Almanac put its own astronomical twist on the term, going back to the 19th century.

More moon shots:

Alan Boyle is NBCNews.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. To keep up with Cosmic Log as well as NBCNews.com's other stories about science and space, sign up for the Tech & Science newsletter, delivered to your email in-box every weekday. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.