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"Blue Moon" Appears in Sky Saturday Night 154

ArbiterOne writes "Tonight a rare spectacle can be seen: the second full moon in a month, which is sometimes called the "blue moon", according to CNN. Don't be disappointed if it isn't actually blue, though; the blueness is caused by increased density of smoke or ash in the air, such as after a volcanic eruption."
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"Blue Moon" Appears in Sky Saturday Night

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  • by Anonymous Coward on Saturday July 31, 2004 @09:43AM (#9852009)
    A "blue moon" is not when there are two full moons in a month. It is when the moon actually turns a shade of blue.

    This is caused by ash or other particles in the air and the light reflecting from the moon is filtered through said air and is 'tinted'.

    Every so often you see a "red moon" when the moon is close to the horizon. The refraction of the light traveling through the atmosphere makes it appear red.

    At least the above was the original definition of "blue moon". Over the years the definition has changed to mean three things [wikipedia.org]. One of which is the two full moons. The later definitions were created more out of ignorance.
  • The Marcels (Score:1, Informative)

    by Anonymous Coward on Saturday July 31, 2004 @09:47AM (#9852028)
    Blue Moon, you saw me standing alone
    Without a dream in my heart
    Without a love of my own

    Blue Moon, you knew just what I was there for
    You heard me saying a prayer for
    Someone I really could care for

    And then there suddenly appeared before me
    The only one my arms will ever hold
    I heard somebody whisper, "Please adore me"
    And when I looked, the moon had turned to gold

    Blue Moon, now I'm no longer alone
    Without a dream in my heart
    Without a love of my own
  • Re:Rare? (Score:5, Informative)

    by severoon ( 536737 ) on Saturday July 31, 2004 @09:48AM (#9852029) Journal

    I heard that the adoption of the term blue moon in modern usage actually stems from a misappropriation of the term from some Native American tribe (around the time frame you mention, early 19th C). The term, as far as my uninformed and caffeine-addled mind can conjure at the moment, originally referred to an occurrence of a particular full moon that occurred during the three-month harvest season; specifically, when four moons occurred during this three month season, the third of the sequence was called a "blue moon". (The Wikipedia entry [wikipedia.org] seems to make reference to this--see the second entry--but I can't find anything specific on it. Also, it doesn't seem to mention the "harvest" season, just any season, which is not what I heard from my unreliable source.)

    This is why our concept of blue moon as the second in a month doesn't seem to make sense in terms of rarity...it's not that rare. It makes a bit more sense if we consider how often four moons occur during the three month harvest season. That was probably quite a bit more rare.

  • by laejoh ( 648921 ) on Saturday July 31, 2004 @10:02AM (#9852079)
    see article [skyandtelescope.com]

    From the article:
    According to Canadian folklorist Philip Hiscock, the term "blue Moon" has been around for more than 400 years, but its modern calendrical meaning has become widespread only in the last 25. And as discovered five years ago, it can be traced to a mistake published in Sky & Telescope in the 1940s!
  • Blue moon explained (Score:3, Informative)

    by hshana ( 657854 ) on Saturday July 31, 2004 @10:03AM (#9852081)
    The term blue moon actually comes from the fact that in old almanacs the second full moon in a month was colored blue on the calendar.
  • by wherley ( 42799 ) * on Saturday July 31, 2004 @10:17AM (#9852145)

    The first moon in July is known as the "Mead Moon" [waningmoon.com].

    A real nice song about the rarity of a Blue Moon is by Nanci Griffith [amazon.com].
  • Re:Rare? (Score:5, Informative)

    by SoSueMe ( 263478 ) on Saturday July 31, 2004 @10:20AM (#9852155)
    Here [com.com] is a really good explanation of the background on our current definition of a "Blue Moon" which seems to have been popularized by none other than Trivial Persuit.

    On July 31 of this year, those taking an evening stroll beneath a cloudless sky will have the opportunity to look up and see what modern folklore refers to as a "blue moon." Though the moon itself will not actually be blue--or likely even appear blue--it will be the second full moon in the same calendar month of July, which is what qualifies this Saturday's lunar view as a blue moon, at least by today's standards.

    That's not to say that the moon has never appeared blue in color to the average, unaided, ground-bound observer. The moon can and has shone blue or even green in color whenever a sufficient quantity of micron-sized particulates is present in the atmosphere, usually after a volcanic eruption.

    The micron-sized debris (specifically, any particles slightly larger than the wavelength of red light, about 0.7 microns) refracts the moonlight, turning it green or blue, based on certain atmospheric factors. For an example of this phenomenon, one need look no further than accounts of blue moons following the eruption of the island of Krakatau in 1883.

    While instances of actual blue-tinted moons represent one of several documented meanings of the term, using blue moon to describe the second full moon in one calendar month is a fairly recent practice. This definition arose in the 20th century, and it didn't really become part of the widespread public consciousness until the 1980s.

    We can attribute this sudden proliferation of a previously undocumented and unused definition for blue moon to three otherwise reputable sources of fine information and fun trivia, all of which were working off bad information.


    What three reputable mass-media trivia resources are most responsible for the current popular definition of a "blue moon" to mean the second full moon in the same calendar month, and what is the likely origin of this "mistaken" definition?

    The most recent and most widely known source of the "new" blue moon definition is none other than the king daddy of all trivia board games, Trivial Pursuit. Specifically, the Trivial Pursuit Genus II edition published in 1986 included this definition as a question in the Science and Nature category.

    Given the popularity of the game, it's little wonder that folklorists witnessed this definition enter widespread usage in the 1980s. But where did the game makers get their information?

    Trivial Pursuit archives (yes, they exist) cite The Kids' World Almanac of Records and Facts, published in 1985, as the source of the question. The book's authors, however, can't trace their own source for this "fact."

    So where did the Almanac authors get it? Folklorist Philip Hiscock suggests it came from our second mass-media source.

    In January 1980, the National Public Radio (NPR) program "Star Date" featured a piece by Deborah Byrd that noted the "second full moon in one calendar month" definition of blue moon. Byrd cited a 1946 article in Sky & Telescope magazine as her source. Hiscock considers the "Star Date" broadcast as the likely source of the Almanac entry, and thus NPR is the second mass-media source to get blue moon "wrong."

    The third, obviously, is the usually reliable Sky & Telescope magazine. A March 1946 article by amateur astronomer James Hugh Pruett titled "Once in a Blue Moon" contains the modern definition of the term, but it cites the 1937 Maine Farmers' Almanac as its source. No edition of that Almanac, however, contains the modern definition of a blue moon.

    Several editions of the Almanac do list a different definition of a blue moon--the third, extra full moon of an agricultural season. The Maine Farmers' Almanacs of tha

  • by Neophytus ( 642863 ) * on Saturday July 31, 2004 @10:30AM (#9852202)
    None: The earth doesn't rely on a calendar so no pattern is changing.
  • by dougmc ( 70836 ) <dougmc+slashdot@frenzied.us> on Saturday July 31, 2004 @10:40AM (#9852247) Homepage
    This whole `second full moon in a month' thing is just stupid. Looks like there's already some interesting comments here about the original source of this idea.

    Fortunately, there is a chance of a real blue moon [reuters.com] if you live near Anchorage, Alaska. Actually, it's not really a fortunate thing, because if this volcano does erupt and spew ash everywhere, it's a big mess. It mucks up your car, you don't want to breath it, it's almost caused airplanes to crash, etc. But it does have the possibility of causing the moon to appear truely blue.

  • by gnu-generation-one ( 717590 ) on Saturday July 31, 2004 @10:50AM (#9852290) Homepage
    "Black Moon is even more rare: When no full moons occur in a month (usually February)"

    That would make it 2018 then?
    Blue moon: 31/Jan/2008, 9am
    Worm moon: 01/Mar/2008, 10pm
    b.t.w. I don't think it's "usually february", I think it is always february. Every month other than february is guaranteed to be longer than the synodic period (about 29.5 days), so is guaranteed to contain a full moon. (apart from the month in which you change from julian to gregorian calendars...)

  • by tootlemonde ( 579170 ) on Saturday July 31, 2004 @10:56AM (#9852315)

    The last time there was no full moon in a month was February, 1999. The event was related to there being a Blue Moon in both January and March of that year.

    Black Moon can also refer to two new moons in one month. The last time it happened was May, 2003. The next time will be December, 2005.

    And let us not forget the Cheshire Moon. This name refers to a new or crescent moon where the line of the crescent looks like a smile or bowl instead of the typical "C" shape.

    The explanation given here: [usatoday.com]

    So, when a Crescent Moon is about to set and the Sun has already set, the Moon points down to the departed Sun: West. The horns poke up and that setting Crescent Moon "grins." If the Moon sets before the Sun, the nearby Sun creates such a glare that we can't see the setting crescent. Then it "frowns, " unseen.

    Nearly the same is true of a rising Crescent Moon. If the rising Crescent rises before the Sun, the Moon points east, down towards the laggard Sun and its horns likewise stick up -- it, too grins. Otherwise, if the crescent rises after the Sun, the Moon frowns unseen.

  • Re:Rare? (Score:5, Informative)

    by srleffler ( 721400 ) on Saturday July 31, 2004 @11:11AM (#9852389)
    Sky and Telescope has published an article more recently, explaining what happened and their role in it. It is available online [skyandtelescope.com].
  • Re:Not all that rare (Score:4, Informative)

    by swimboy ( 30943 ) on Saturday July 31, 2004 @11:31AM (#9852472)
    The moon's cycle is about 29.5 days, which makes about 12.4 full moons a year. That means a blue moon about every 3 years.

    The 17 blue moons in 20 years is due to two different definitions of what constitutes a blue moon. So, blue moons are twice as common, because there are two different ways to define what a blue moon is!
  • Re:Not all that rare (Score:3, Informative)

    by kzinti ( 9651 ) on Saturday July 31, 2004 @11:42AM (#9852522) Homepage Journal
    The lunar cycle is 29.5 days long on average, not 28. That gives about 12.4 full moons per year, on average.

    I don't know how infoplease.com counted blue moons to get 17 in the next twenty years, unless it was counting both the 2nd-in-a-month and the 4th-in-a-season varieties. Ask this blue moon calculator [obliquity.com] to list the blue moons between 2004 and 2024, and it lists nine of them (of the 2nd-in-a-month kind).

    That's about every 2.2 years.
  • by gnu-generation-one ( 717590 ) on Saturday July 31, 2004 @11:52AM (#9852577) Homepage
    "Black Moon is even more rare: When no full moons occur in a month (usually February)"

    Of course, as someone pointed out, a "back moon" would imply
    two blue moons in that year [blibbleblobble.co.uk]

    So are we supposed to give them different names, or is it not possible to uniquely identify each moon in 2018? January Blue Moon and March Blue Moon or something?

    And can you change when blue moons occur by selecting an appropriate timezone, or by changing to daylight-savings-time just before a full moon?
  • by jks ( 269 ) on Saturday July 31, 2004 @12:18PM (#9852714) Homepage
    See also a pretty photo [nasa.gov], along with some explanations of the term "blue moon".
  • by Anonymous Coward on Saturday July 31, 2004 @12:53PM (#9852896)
    A smiling crescent moon can only be seen in tropical or near tropical latitudes. In order for there to be a vertical crescent moon the sun must be directly below the moon, and this only occurs where the ecleptic is close to vertical. The only time I have seen one is when I was in Hawaii a few years ago.
  • by kzinti ( 9651 ) on Saturday July 31, 2004 @12:59PM (#9852927) Homepage Journal
    Factors that affect tides are the moon's distance from the earth, and its alignment relative to the sun. Tides are higher when the moon is at perigee (when its orbit brings it closest to the earth). Tides are also higher when the sun, moon, and earth align with the sun and moon on the same side of earth. The gravitational forces due to sun and moon add up to produce higher tides. The latter affect would occur at new moon; don't know if the former has any relationship to the lunar phases. Neither affect would have any relationship to "blue moons", which are an artifact of our calendar.
  • Re:Not all that rare (Score:2, Informative)

    by LC Gundo ( 651469 ) * on Saturday July 31, 2004 @07:37PM (#9855040) Journal
    According to the CNN article the original definition is the 3rd full moon in a quarter that has 4 full moons, so tonight meets both the original Maine Farmer's Almanac definition and the post-1980 Sky and Telescope magazine definition.

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