Blue moon

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This article is about an additional full moon that appears in a subdivision of a year. For other uses, seeBlue Moon (disambiguation).

Blue moon of theDecember 2009 lunar eclipse

Ablue moonis an additionalfull moonthat appears in a subdivision of a year: either the third of four full moons in a season, or a second full moon in a month of the common calendar.

The phrase has nothing to do with the actual color of the moon, although a literal blue moon (the moon appearing with a tinge of blue) may occur in certain atmospheric conditions: e.g., if volcanic eruptions or fires leave particles in the atmosphere of just the right size to preferentially scatter red light.[1]

The term has traditionally referred to an extra full moon, where a year which normally has 12 full moons has 13 instead. The blue moon reference is applied to the third full moon in aseasonwith four full moons,[2]thus correcting the timing of the last month of a season that would have otherwise been expected too early. This happens every two to three years (seven times in theMetonic cycleof 19 years).[3]The March 1946 issue ofSky & Telescopemisinterpreted the traditional definition, which led to the modern colloquial misunderstanding that a blue moon is a secondfull moonin a singlesolar calendarmonth with no seasonal link.

Owing to the rarity of a blue moon, the term blue moon isused colloquially to mean a rare event, as in the phrase once in a blue moon.[4][5]

Onelunation(an average lunar cycle) is 29.53days. There are about 365.24 days in atropical year. Therefore, about 12.37 lunations (365.24 days divided by 29.53 days) occur in a tropical year. In the widely usedGregorian calendar, there are 12months(the wordmonthis derived frommoon[6]) in a year, and normally there is one full moon each month. Each calendar year contains roughly 11 days more than the number of days in 12 lunar cycles. The extra days accumulate, so every two or three years (seven times in the 19-yearMetonic cycle), there is an extra full moon. The extra full moon necessarily falls in one of the four seasons, giving that season four full moons instead of the usual three, and, hence, a blue moon.

Incalculatingthe dates forLentandEaster, Catholicclergyidentified a Lenten moon. Historically, when the moons arrived too early, they called the early moon a betrayer (

, so the Lenten moon came at its expected time.

according to its time of year. The occasional 13th full moon that came too early for its season was called a blue moon, so the rest of the moons that year retained their customary seasonal names.

called the third full moon in a season that had four the blue moon.

The frequency of a blue moon can be calculated as follows. It is the period of time it would take for an extrasynodic orbitof the moon to occur in a year. Given that a year is approximately 365.2425 days and a synodic orbit is 29.5309 days,

then there are about 12.368 synodic months in a year. For this to add up to another full month would take 1/0.368 years. Thus it would take about 2.716 years, or 2 years, 8 months and 18 days for another blue moon to occur.

Using the common Sky & Telescope misunderstanding, when one calendar month has two full moons; the second one is called a blue moon. On rare occasions in a calendar year (as happened in 2010 in time zones east of UTC+07), both January and March each have two full moons, so that the second one in each month is called a blue moon; in this case, the month of February, with only 28 or 29 days, has no full moon. Under this misinterpretation a blue moon can be more frequent.

Blue moon of August 31, 2012, viewed fromSlobozia, Romania.

The suggestion has been made that the term blue moon for intercalary month arose byfolk etymology, the blue replacing the no-longer-understoodbelewe, to betray. The original meaning would then have been betrayer moon, referring to a full moon that would normally (in years without an intercalary month) be the full moon of spring, while in an intercalary year, it was traitorous in the sense that people would have had to continue fasting for another month in accordance with the season ofLent.[8][9]

The earliest recorded English usage of the termblue moonis found in an anti-clerical pamphlet (attacking the Roman clergy, and cardinalThomas Wolseyin particular) by twoconvertedGreenwich friars, William Roy and Jerome Barlow, published in 1528 under the titleRede me and be nott wrothe, for I say no thynge but trothe. The relevant passage reads:[10]

O churche men are wyly foxes […] Yf they say the mone is blewe / We must beleve that it is true / Admittynge their interpretacion.[11]

It is not clear from the context that this refers tointercalation; the context of the passage is a dialogue between two priests servants, spoken by the character Jeffrey (a brefe dialoge betwene two prestes servauntis, named Watkyn and Ieffraye). The intention may simply be that Jeffrey makes an absurd statement, the moon is blue, to make the point that priests require laymen to believe in statements even if they are patently false. But in the above interpretation of betrayer moon, Jeffrey may also be saying that it is up to the priests to say when Lent will be delayed, by announcing blue moons which laymen have no means to verify.

In the 19th and early 20th centuries, theMaine Farmers Almanaclisted blue moon dates for farmers. These correspond to the third full moon in a quarter of the year when there were four full moons (normally a quarter year has three full moons).Full moon nameswere given to each lunation in a season. The seasons used were those of themean tropical year, equal in length, as opposed to the astronomical seasons which vary in length because the earths speed in its orbit round the sun is not uniform.

To compare, in 1983 the equal seasons began at 1.48 AM on 23 March, 9.15 AM on 22 June, 4.42 PM on 21 September and 12.10 AM on 22 December, while the astronomical seasons began at 4.39 AM on 21 March, 11.09 PM on 21 June, 2.42 PM on 23 September and 10.30 AM on 22 December (all times GMT). When a season has four full moons the third is called the blue moon so that the last can continue to be called with the proper name for that season.[2]

The March 1946Sky and Telescopearticle Once in a Blue Moon by James Hugh Pruett misinterpreted the 1937Maine Farmers Almanac. Seven times in 19 years there were and still are 13 full moons in a year. This gives 11 months with one full moon each and one with two. This second in a month, so I interpret it, was called Blue Moon. Widespread adoption of the definition of a blue moon as the second full moon in a month followed its use on the popular radio programStarDateon January 31, 1980[2]and in a question in theTrivial Pursuitgame in 1986.[5]

The most literal meaning ofblue moonis when the moon (not necessarily a full moon) appears to a casual observer to be unusually bluish, which is a rare event. The effect can be caused by smoke or dust particles in the atmosphere, as has happened after forest fires in Sweden and Canada in 1950 and 1951,[12]and after theeruption of Krakatoa in 1883, which caused the moon to appear blue for nearly two years. Other less potent volcanoes have also turned the moon blue. People saw blue moons in 1983 after the eruption of theEl Chichnvolcano in Mexico, and there are reports of blue moons caused byMount St. Helensin 1980 andMount Pinatuboin 1991.[13]In the Antarctic diary ofRobert Falcon Scottfor July 11, 1911 his entry says, … the air thick with snow, and the moon a vague blue.[14]On that date the moon phase would have looked full.

On September 23, 1950, severalmuskegfires that had been smoldering for several years in Alberta, Canada, suddenly blew up into majorand very smokyfires. Winds carried the smoke eastward and southward with unusual speed, and the conditions of the fire produced large quantities of oily droplets of just the right size (about 1micrometrein diameter) to scatter red and yellow light. Wherever the smoke cleared enough so that the sun was visible, it was lavender or blue. Ontario, Canada, and much of the east coast of the United States were affected by the following day, and two days later, observers in Britain reported an indigo sun in smoke-dimmed skies, followed by an equally blue moon that evening.[13]

The key to a blue moon is having lots of particles slightly wider than the wavelength of red light (0.7 micrometer)and no other sizes present. It is rare, but volcanoes sometimes produce such clouds, as do forest fires. Ash and dust clouds thrown into the atmosphere by fires and storms usually contain a mixture of particles with a wide range of sizes, with most smaller than 1 micrometer, and they tend to scatter blue light. This kind of cloud makes the moon turn red; thus red moons are far more common than blue moons.[15]

The following blue moons occur between 2009 and 2021. These dates useUTCas the timezone; exact dates vary with different timezones.

Using theMaine Farmers Almanacdefinition of blue moon (meaning the third full moon in a season of four full moons, but referenced to astronomical rather than equal seasons), blue moons have occurred or will occur on:

Unlike the astronomical seasonal definition, these dates are dependent on the Gregorian calendar and time zones.

Two full moons in one month (the second of which is a blue moon):[16]

2009: December 2 and 31 (partial lunar eclipsevisible in some parts of the world), only in time zones west ofUTC+05.

2010: January 1 (partial lunar eclipse) and 30, only in time zones east ofUTC+04:30.

2010: March 1 and 30, only in time zones east ofUTC+07.

2012: August 2 and 31, only in time zones west ofUTC+10.

2012: September 1 and 30, only in time zones east ofUTC+10:30.

2018: January 2 and 31, only in time zones west of UTC+11.

2018: March 2 and 31, only in time zones west of UTC+12.

2020: October 1 and 31, only in time zones west of UTC+10.

The next timeNew Years Evefalls on a Blue Moon (as occurred on December 31, 2009 in time zones west of UTC+05) is after one Metonic cycle, in 2028 in time zones west of UTC+08. At that time there will be atotal lunar eclipse.

Blue moons have been referenced in popular culture.

Blue Moonis a popular music standard, written by Richard Rodgers and Lorenz Hart in 1934,[17]and one of the best knownfootball chants,[18]used since the 90s byManchester CityandCrewe Alexandra.[19]Once in a Very Blue Moonis a song written byPatrick Alger, recorded byNanci Griffith, and released on her 1984 LP of the same name.New Blue Moon, released in 1990, was a song written and recorded by theTraveling Wilburys. There are more modern songs, likeBecks 2014Blue Moon.[17][20]South Koreanrock bandCN Bluenamed their 2013-2014 concert tourBlue Moon World Tour..[21]Blue Moon of Kentuckyis a bluegrass standard, written in 1946 byBill Monroe.

In the 1998 paranormal romance fiction novel byLaurell K. Hamiltonof the same name,Blue Moonrefers to two full moons occurring within the same month.[22]In the 2009 young adult fiction novel byAlyson Noëlof the same name,Blue Moonrefers to two full moons occurring within the same month and the same astrological sign.[23]Note that if two full moons fall within the same astrological sign they will fall in different calendar months, andvice versa. In the novels ofSimon R. Greenthe blue moon plays a significant magical role, and also figures in titles of three of his novels:Blue Moon Rising,Beyond the Blue Moon, andOnce in a Blue Moon, all of the Hawk & Fisher fantasy series.

The Moon Is Blue, a 1953 movie starring William Holden, was nominated for three Oscars.[24]Blue Moon Investigations is the name of the detective agency in the TV seriesMoonlightingstarringCybill ShepherdandBruce Willis.[25]A Blue Moon appears as a significant element in the 2011 filmThe Smurfs,[26]and the Wikipedia page on Blue Moon is viewed in the movie.The SmurfsTV show also featured the blue moon in an episode.[27]The theme song forThe SopranosWoke Up This MorningbyAlabama 3, references a blue moon in your eyes in its lyrics. Once in a Blue Moon is also the name of an episode of TV showCharmed, which involves the three witches being affected by the blue moon magically, and turning into monsters.[28]

Blue moon is the name of a country in NintendosAdvance Wars series.

Gibbs, Philip (May 1997).Why is the sky blue?.

… may cause the moon to have a blue tinge since the red light has been scattered out.

Sinnott, Roger W.; Olson, Donald W.; Fienberg, Richard Tresch (May 1999).Whats a Blue Moon?.

The trendy definition of blue Moon as the second full Moon in a month is a mistake.

Plait, Phil.Todays Full Moon is the 13th and Last of 2012.

Smith, Bridie (December 28, 2009).Once in a Blue Moon …

Hiscock, Philip (August 30, 2012).Folklore of the Blue Moon

Espanek, Fred.Eclipses and the moons orbit.

. Almanac Publishing Co. August 24, 2009

Frequently asked questions about the date of Easter. Oikoumene.org (2007-01-31). Retrieved on Aug ust 14, 2012.

April 1, 2004, at theWayback Machine.. Astro.nmsu.edu. Retrieved on August 14, 2012

printed by John Schott at Strasburg in 1528. See also

Koelbing, Arthur (190721).Barclay and Skelton: German Influence on English Literature. In A.W. Ward; et al.

The Cambridge History of English and American Literature

. New York: G.P. Putnams Sons. vol.III, ch.4, 14.ISBN1-58734-073-9.

Minnaert, M: De natuurkunde van t vrije veld 5th edition Thieme 1974, part I Licht en kleur in het landschap par.187;ISBN90-03-90844-3(out of print); also seeISBN0-387-97935-2

Blue Moon. science.nasa.gov (July 7, 2004).

Bowling, S. A. (1988-02-22).Blue moons and lavender suns. Alaska Science Forum, Article 861

Joffe, Justin (July 31, 2015).The Blue Moons Rich History in American MusicThe New York Observer

Keidel, Phil (September 18, 2013).20 Chants Every True Manchester City Fan Should KnowBleacher Report

Brobyn, Emily (March 9, 2011).Blue Moon Significance

Grow, Kory (January 20, 2014).Beck Admits Hes Tired of Being Alone in New Song Blue Moon

Bae, Soo-min (4 March BLUE unveils 2013 BLUE MOON World Tour.

. New York City: Ace Books. pp.Ch. 46.ISBN0-441-00574-8.

. New York: St. Martins Griffin. pp.Ch. 37.ISBN0-312-53276-8.

Moore, Roger (July 29, 2011).Smurfs in 3-D? Not as scary as you might thinkChicago Tribune

The Smurfs Season 3 Episode 1 Once In A Blue MoonTV.com

Charmed Season 7 Episode 6: Once in a Blue MoonTV.com

Information about the August 2012 Blue Moon

Folklore of the Blue Moonby Philip Hiscock

Whats a Blue Moon?by Donald W. Olson, Richard T. Fienberg, and Roger W. Sinnott,

. Article explaining that originally a blue moon meant the 3rd full moon in a season of 4 full moons, and how the 2nd in a month error began.

Blue moon calculatorby David Harper

Its a big night for a blue moonat nbcnews.com

What does blue moon really mean?blog entry on lunar calendars and computing

Blue moon definition based on a mistakeby Tony Rice

This page was last edited on 1 July 2018, at 18:27

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