Blue moon 316038 223415847 2008-07-03T23:51:40Z ClueBot 4928500 Reverting possible vandalism by [[Special:Contributions/71.172.26.97|71.172.26.97]] to version by 70.254.167.92. False positive? [[User:ClueBot/FalsePositives|Report it]]. Thanks, [[User:ClueBot]]. (432104) (Bot) ''This article is about the astronomical phenomenon. For other uses, see [[Blue Moon (disambiguation)]].'' The term '''''blue moon''''' is commonly used [[metaphor]]ically to describe a rare event, as in the saying "once in a blue moon". A blue moon is actually a name given to an irregularly timed [[full moon]]. Most years have twelve full moons which occur approximately monthly, but each calendar year contains those twelve full lunar cycles plus about eleven days to spare. The extra days accumulate, so that every two or three years there is an extra full moon (this happens every 2.72 years). Different definitions place the ''extra'' moon at different times - the extra moon is called a "blue moon". *Folklore gave each moon a name according to its time of year. A moon which came too early had no folk name - and was called a ''blue moon''. *The [[Farmer's Almanac]] defined ''blue moon'' as an extra full moon that occurred in a season(which would normally have three full moons). If a season had 4 full moons, the 3rd full moon was named a ''blue moon''. *Until 1999, the common definition of ''blue moon'' was the 2nd full moon in a calendar month (this was a misinterpretation of the Maine Farmer's Almanac in 1946 that became commonly accepted and was discovered in 1999). The moon has also literally had a visible blue coloring on rare occasions, caused by atmospheric disturbances. ==Early English and Christian Usage== The earliest recorded English usage of the term "Blue moon" was in 1528 in a pamphlet violently attacking the English Clergy,<ref>{{cite web |first=Arthur, Ph.D. |last=Koelbing |url=http://www.bartleby.com/213/0414.html |title=Barclay and Skelton: German influence on English literature |work=The Cambridge History of English and American Literature, Volume III |year=1907–21 |publisher=[[Bartleby.com]]}}</ref> entitled ''Rede Me and Be Not Wrothe'' ''[Read me and be not angry]'': "Yf they say the mone is belewe / We must beleve that it is true" ''[If they say the moon is blue, we must believe that it is true]''. Some interpret this "Blue Moon" as relating to absurdities and impossibilities,<ref>{{cite web |url=http://www.ips-planetarium.org/planetarian/articles/folkloreBlueMoon.html |title=Folklore of the "Blue Moon" |first=Philip |last=Hiscock |publisher=[[International Planetarium Society]] |date=[[19 June]] [[2006]]}}</ref> and a similar moon-related adage was first recorded in the following year: "They would make men beleue ... that þe Moone is made of grene chese". ''"They would make men believe ... that the moon is made of green cheese"''. An alternative interpretation uses the other old-English meaning of "belewe" (which can mean "Blue", or "Betrayer")<ref>{{cite web |url=http://www.farmersalmanac.com/what-is-a-blue-moon |title=What is a "Blue Moon"? |publisher=[[Farmers' Almanac]]}}</ref> The church was responsible for the calendar and used the complex [[computus]] to calculate the most important date of Easter, which is based on the full moon. Lent falls before Easter starting at the beginning of the [[Lent moon]] cycle (late Winter moon). The next moon is the [[Egg moon]] (early Spring moon) and Easter usually falls on the first Sunday after the full Egg moon. The Clergy were responsible for telling people when it was Lent & Easter - it was critical to celebrate Lent, the trials and resurrection of Christ at the correct time. Every 2 to 3 years the Lent and Egg moons would come too early, the Clergy would have to tell people whether the moon was the Lent moon or a false one - they may have called this a "Betrayer moon". ==Visibly blue moon== The most literal meaning of ''blue moon'' is 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, notably, after the eruption of [[Krakatoa]] in 1883, which caused the moon to appear blue for nearly two years. ==Folklore== Full moons were given names in folklore, twelve each year, corresponding to times of the year and the related weather and crop needs - with folk names such as [[Harvest moon]], [[Growing moon]], and [[Snow moon]] (varying widely with locality & culture - see other [[full moon]] names). A year has slightly more than 12 full moons, so in the years with 13 full moons, one moon would not align with the correct season and was named a blue moon, which then re-aligned the rest of the year's twelve moons (so that corn was planted and harvested at the correct seasonal time, and so on). The origin of the term ''blue moon'' is steeped in folklore, and its meaning has changed and acquired new nuances over time. Some folklore said that when there was a blue moon, the moon had a face and talked to the items in its moonlight. ==Farmer's Almanac blue moons== In the 1800s and early 1900s, the Maine [[Farmer's Almanac]] listed Blue Moon dates for farmers. These correspond to the third full moon in a quarter of the year when there were four full moons &ndash; normally a quarter year has three full moons. Names are given to each moon in a [[season]] - for example, the first moon of summer is called the early summer moon. The second is called the mid summer moon. The last is called the late summer moon. When a season has four moons the third is called the blue moon so that the last can continue to be called the late summer moon. The division of the year into quarters starts with the nominal Vernal [[equinox]] - on or around March 21.<ref>{{cite web |last=Clarke |first=Kevin |year=1999 |url=http://www.inconstantmoon.com/cyc_blue.htm |title=on blue moons |publisher=InconstantMoon.com}}</ref> This is close to the astronomical [[season]]s but follows the Christian [[computus]] used for calculations of Easter (this places each equinox evenly between the Summer & Winter [[solstice]]s to calculate seasons, rather than using the actual [[equinox]]). Some naming conventions keep the moon's seasonal name for its entire cycle - from its appearance as a [[new moon]], through the full moon in the middle, to the next new moon. In this convention a blue moon starts with a new moon and continues until the next new moon starts the late season moon. To calculate the moon names for the seasons using the appearance of the new moon: #Locate the new moons that are nearest to the [[solstices]] and [[equinoxes]]. These are the early season moons. Mark the new moons as follows: nearest December 21 - the early winter moon, nearest March 20 - the early spring moon, nearest June 20 - the early summer moon, nearest September 22 - the early fall moon. '''Note:''' This makes the full moon of that season about 2 weeks later, always after the 20th or 21st of the month. #Locate the new moons following the ones marked above. Mark them as the mid season moons. For example, the new moon that follows the early winter moon is marked as the mid winter moon. This is most often in January. #Locate the new moons before the ones marked in step 1. Mark them as the late season moons of the previous season. For example, the new moon that precedes the early winter moon is the late fall moon. This is most often in November. #Locate all new moons that have not been marked either early, mid, or late moons. These are the blue moons. Seasons are reversed in the southern hemisphere. Adjust the above instructions for your location. This definition was used until 1946, when the dates and meaning provided by the Farmer's Almanac were misinterpreted in popular products (after its editors had died), and was only recovered in 1999.<ref name="SkyTel">{{cite web |last=Sinnott |first=Roger W., Donald W. Olson, and Richard Tresch Fienberg |url=http://skyandtelescope.com/observing/objects/moon/article_127_1.asp |title=What's a Blue Moon? |publisher=''[[Sky & Telescope]]'' |month=May |year=1999 |accessdate=2008-02-09 |quote=The trendy definition of "blue Moon" as the second full Moon in a month is a mistake.}}</ref> According to this calculation the year 2008 has one blue moon that occurs in the spring. For the year 2008, these are the dates of the moons in the northern hemisphere. These dates use the actual solstices and not the artificial solstices that give each season an equal number of days. #January 8 - February 5 → Mid Winter moon #February 6 - March 6 → Late Winter moon #March 7 - April 4 → Early Spring moon #April 5 - May 4 → Mid Spring moon #May 5 - June 2 → '''Blue moon''' (full Blue Moon on May 20) #June 3 - July 2 → Late Spring moon #July 3 - July 31 → Early Summer moon #August 1 - August 29 → Mid Summer moon #August 30 - September 28 → Late Summer moon #September 29 - October 27 → Early Fall moon #October 28 - November 26 → Mid Fall moon #November 27 - December 26 → Late Fall moon ==Calendar blue moons== From 1946, people started calling a full moon a ''blue moon'' if it was the second of two full moons to occur in the same calendar month. This definition of ''blue moon'' originated from a mistake in an article in the March 1946 ''[[Sky & Telescope]]'' magazine, which misinterpreted the dates & meaning provided by the [[Farmer's Almanac]]. It was helped to popularity when [[Earth & Sky]] used this definition in the radio series Star Date for some years, and as a result the game [[Trivial Pursuit]] used it in a question and answer about blue moon. It was recovered only in 1999 when researchers for ''[[Sky & Telescope]]'' magazine discovered the error. They noticed that the ''Maine [[Farmer's Almanac]]'' from 1829 to 1937 reported blue moons that did not fit the meaning of the term ''calendar blue moon''.<ref name="SkyTel" /> ''[[Sky & Telescope]]'' printed a retraction and correction though by this time the calendar definition was in common use. Calendar Blue moons occur infrequently, in years with thirteen full moons. There are also some years in which there is no full moon in February at all, since February is slightly shorter than the time from one full moon to the next. This condition, known as a [[black moon]], gives additional 'blue' moons in the preceding and following months (namely January and March). The last time this occurred was in 1999, and the next occurrence will be in 2018, according to UTC. The previous calendar blue moon (based on [[Coordinated Universal Time|UTC]]) was on [[June 30]], [[2007]]. The first full moon would have occurred on [[June 1]], [[2007]]. That was [[May 31]], [[2007]] in the Western Hemisphere, making that full moon the second occurrence in May in the Western Hemisphere (see below); the next calendar blue moon will be [[December 31]], [[2009]]. ===Time zone problems=== Occasionally whether a moon is called ''blue'' depends on the time zone. Any [[full moon]] occurs simultaneously everywhere, but at that moment clocks and calendars are ''not'' the same. Example, when it is early evening on August 31 in [[Europe]], it is already early morning September 1 in [[New Zealand]]. Hence, residents of [[London]] seeing a full moon when their clocks and calendar say it is August 31 would call what they see a calendar ''blue moon''. People seeing the same full moon from [[Auckland]] would note by their clocks and calendar that it is the early morning of September 1, and they would ''not'' term it a ''blue moon''. But they would probably have a calendar ''blue moon'' at the end of September, or perhaps October.<ref name="obli">{{cite web |url=http://www.obliquity.com/astro/blue2007.html |title=The Blue Moon of 2007 |publisher=Obliquity.com |date=[[13 October]] [[2007]] |last=Harper and Stockman}}</ref> Because this is confusing, astronomers worldwide and the calendar makers who rely on them typically choose the time zone of the [[Royal Greenwich Observatory]] in the [[United Kingdom]], known as [[Greenwich Mean Time]], or the nearly identical [[Coordinated Universal Time|UTC]] time zone. As a practical matter, because the moon seems to the casual viewer to be full for almost three days, the use of a foreign time zone for calendar markings for ''full'' moons makes little difference. ==Blue Moons between 2005 and 2015== The following Blue Moons occur between 2005 and 2015. These dates use UTC as the timezone, months will vary with different timezones. Using the Farmer's Almanac definition of blue moon (meaning the third full moon in a season of four full moons) blue moons occur: * [[August 19]], [[2005]] * [[May 19]], [[2008]] * [[November 21]], [[2010]] * [[August 21]], [[2013]] If the "Calendar Blue Moon" (1946-1999) definition is taken (meaning the second full moon in any given month) then blue moons occur [http://www.obliquity.com/cgi-bin/bluemoon.cgi]: *[[June 30]], 2007 *[[December 31]], 2009 *[[August 31]], 2012 *[[July 31]], 2015 Note that the year 2018 (as well as 2037, 1961, 1942, 1999 etc.) will have a black moon (no full moon in the short month of February) - and this results in 2 blue moons in January and March. ==See also== * [[Black moon]] * [[Wet moon]] * [[Full moon]] * [[New moon]] * [[Half moon]] * [[Lunar phase#Names of lunar phases|Rising crescent moon]] * [[Lunar phase#Names of lunar phases|Crescent moon]] * [[Lunar phase#Names of lunar phases|Gibbous moon]] * [[Harvest moon]] * [[Lunar phase]] * [[Hunter's moon|Blood moon]] ''(also known as Hunter's moon)'' * [[Fairy moon]] ==References== * ''[[Oxford English Dictionary]]'' ===Notes=== {{Reflist}} ==External links== * [http://www.netaxs.com/~mhmyers/blue/blue.html ''What is a Blue Moon?'' by Michael Myers] * [http://www.ips-planetarium.org/planetarian/articles/folkloreBlueMoon.html ''Folklore of the Blue Moon'' by Philip Hiscock] * [http://skyandtelescope.com/observing/objects/moon/article_127_1.asp ''What's a Blue Moon?'' by Donald W. Olson, Richard T. Fienberg, and Roger W. Sinnott - Sky & Telescope] * [http://www.infoplease.com/spot/bluemoon1.html ''Once in a Blue Moon - What is a blue moon?'' by Ann-Marie Imbornoni] * [http://www.worldwidewords.org/topicalwords/tw-blu2.htm ''Topical Words - Blue Moon''] * [http://www.wilsonsalmanac.com/bluemoon.html ''Blue Moon: Folklore or fakelore?'' by Pip Wilson] * [http://www.obliquity.com/cgi-bin/bluemoon.cgi ''A Blue Moon Calculator'' by David Harper] * [http://www.inconstantmoon.com/cyc_blue.htm ''On Blue Moons'' by Kevin Clarke] * [http://skytonight.com/observing/objects/moon/3304131.html Article arguing that a blue moon is the 3rd full moon in a season of 4 blue moons, not the 2nd in a month] * [http://www.uranometrianova.pro.br/astronomia/AA001/bluemoon.htm ''Blue Moon'' by Irineu Gomes Varella (Portuguese)] * [http://www.farmersalmanac.com/astronomy/bluemoon.html ''What is a Blue Moon?''] * [http://www.msnbc.msn.com/id/18869948/ '''Blue moon' coming to our skies soon''] [[Category:Phases of the Moon]] [[Category:Calendars]] [[Category:Moon myths]] [[da:Blå måne]] [[de:Blue Moon (Astronomie)]] [[es:Luna azul (segunda Luna Llena)]] [[ja:ブルームーン]] [[pt:Lua azul]] [[sv:Blå måne]]