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75-442: The calendrical meaning of "blue moon" is unconnected to the other meanings. It is often referred to as “traditional”, but since no occurrences are known prior to 1937 it is better described as an invented tradition or “modern American folklore”. The practice of designating the second full moon in a month as "blue" originated with amateur astronomer James Hugh Pruett in 1946. It does not come from Native American lunar tradition , as

150-489: A 532-year period of Easter dates. Given that all possible dates on which Easter can occur lie within a 35-day period – from March 22 to April 25 (old style dates) or from April 4 to May 8 (new style dates) – the Alexandrian Easter algorithm is equivalent to 18620 options (532 x 35), showing the complexity of computus implementation in a compact clockwork. The Gregorian Easter algorithm gives even more options due to

225-458: A Pruett 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 a total lunar eclipse . Calendrical calculation A calendrical calculation is a calculation concerning calendar dates . Calendrical calculations can be considered an area of applied mathematics . Some examples of calendrical calculations: Calendrical calculation

300-475: A computer to print calendar and diary pages for past or future sequences of any desired length from the reform of the calendar, which in England was 3/14 September 1752. The article Date of Easter gives algorithms for calculating the date of Easter. Combining the two enables the page headers to show any fixed or movable festival observed on the day, and whether it is a bank holiday. The algorithm utilises

375-455: A dial for 6 moveable feasts and a perpetual calendar with date, day of the week, month and bissextile year indicators. The Easter date in a computus clock with an opto-mechanical indication is shown by the superposition of the matching holes of perforated discs. This type of display has also been used to indicate the date of Orthodox Easter. An opto-mechanical Easter date display was built into this “Easter of Christ Computus Clock” clock of 2005,

450-621: A few examples have ever been produced. The world's first computus module, realizing the Gregorian computus algorithm, was invented, designed and made by the French clockmaker Jean-Baptiste Schwilgué (“Comput ecclésiastique”, 1821, which was stolen from Strasbourg Cathedral in 1944, with the present location unknown). Subsequently, separated computus modules were made by the Danish clockmaker Jens Olsen (also called “Comput ecclésiastique”; 1924), and by

525-583: A given year in a fifteen-year period). The computations after the Gregorian reform of 1582 should also take into account additional corrections necessary due to particularities of the Gregorian calendar , notably the solar equation (taking into account some non-leap century years) and the lunar equation (for correction of the Metonic cycle) The term “computus” as the description of the Easter date computation

600-510: A month, so I interpret it, was called Blue Moon”. In 1980 the term was used (with Pruett’s definition) in a U.S. radio program, Star Date , and in 1985 it appeared in a U.S. children’s book, The Kids' World Almanac of Records and Facts (“What is a blue moon? When there are two full moons in a month, the second one is called a blue moon. It is a rare occurrence.”) In 1986 it was included as a question in Trivial Pursuit (likely taken from

675-580: A person sees a blue moon and makes a wish, he will be granted a second chance in things.” In 1999 folklorist Philip Hiscock presented a timeline for the calendrical term. First, the August page of the 1937 Maine Farmers' Almanac ran a sidebar claiming that the term was used “in olden times” for an extra full moon in a season, and gave some examples (21 November 1915, 22 August 1918, 21 May 1921, 20 February 1924, 21 November 1934, 22 August 1937, and 21 May 1940). Six years later, Laurence J. Lafleur (1907-66) quoted

750-456: A program cam wheel, since the complicated design of a counting computus makes it difficult to integrate into the compact movement of a pocket watch and, in particular, a wristwatch. The only known example of a pocket watch with an indication of the Easter date according to the Gregorian calendar is the supercomplication “ Calibre 89 ” pocket watch by the Swiss company Patek Philippe . Four copies of

825-570: A question in the Trivial Pursuit game in 1986. Several songs have been titled "Blue Moon", seen as a "symbol of sadness and loneliness." The moon (and sun) can appear blue under certain atmospheric conditions – for instance, if volcanic eruptions or large-scale fires release particles into the atmosphere of just the right size to preferentially scatter red light. According to the Encyclopaedia Britannica, scattering

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900-406: A separate computus module (“Comput ecclésiastique”), that has certain similarities to Schwilgué's “Comput ecclésiastique”. Later, in 1928, Jens Olsen made the calculations of a supercomplicated astronomical computus clock. The clock, known as “ World Clock ” (in Danish, “Verdensuret”), was finished in 1955, 10 years after his death, by his colleague Otto Mortensen, who took over the project. The clock

975-520: A similar effect. The Antarctic diary of Robert Falcon Scott for July 11, 1911 mentioned "the air thick with snow, and the moon a vague blue". The key to a blue moon is having many particles slightly wider than the wavelength of red light (0.7 micrometer)—and no other sizes present. 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

1050-463: A single year (1915, 1961, 1999, 2018, 2037, 2094). 1915 had four blue moons (two Pruett, one Maine, one astro-seasonal). 1934 and 2048 have three (one of each type). Despite the 187 blue moons appearing across the 200 years in this table, only 146 years have any of these 3 types of blue moons, leaving 54 years (thus averaging just over 1 year in every 4) which have none of the 3 rules represented in that calendar year. While not totally unexpected (given

1125-531: 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 Pruett blue moon to occur. Or approximately once in 32.5 months on an average. When there are two Pruett blue moons in a single year, the first occurs in January and the second in March or April. The next time New Year's Eve falls on

1200-535: A “blue moon / Low in the west.” It was written at a time when the eruption of Mount Tambora was causing global climate effects, and not long before the first recorded instances of “blue moon” as a metaphor. The OED cites Pierce Egan’s Real Life in London (1821) as the earliest known occurrence of “blue moon” in the metaphorical sense of a long time. (“How's Harry and Ben?—haven't seen you this blue moon.”) An 1823 revision of Francis Grose’s ‘’Classical Dictionary of

1275-436: Is a stub . You can help Misplaced Pages by expanding it . Computus clock A computus clock is a clock equipped with a mechanism that automatically calculates and displays, or helps determine, the date of Easter (and other dependent dates of moveable Church feasts ). A computus watch carries out the same function. The movement of a computus clock provides and/or calculates astronomical and calendar information according to

1350-486: Is an unparalleled tabular calendar showing the dates and days of the week of all 12 months of the year, the phases of the Moon for every date, and the dates of Easter and other moveable feasts. The computus and Gregorian perpetual calendar automatically switch at midnight at New Year to calculate the calendar for the following year. The French clockmaker Daniel Marius Vachey  [ fr ] also took his inspiration from

1425-478: Is displayed in Copenhagen's Rådhus (City Hall). The computus of Jens Olsen's World Clock has 5 ecclesiastical functions – the Gregorian dominical letter, the Gregorian epact, the 28-year solar cycle, the indiction and the golden number, while the clock is also equipped with a Gregorian perpetual calendar indicating the date, day of the week, month and the year in four digits. Beneath the ecclesiastical dials there

1500-413: Is further supported by the spurious explanation the almanac gave: The Moon usually comes full twelve times in a year, three times in each season... However, occasionally the moon comes full thirteen times in a year. This was considered a very unfortunate circumstance, especially by the monks who had charge of the calendar. It became necessary for them to make a calendar of thirteen months, and it upset

1575-636: Is one of the five major Savant syndrome characteristics. Numerical methods were described in the Journal of the Department of Mathematics, Open University, Milton Keynes, Buckinghamshire (M500) in 1997 and 1998. The following algorithm gives the number of days ( d ) in month m of year y . The value of m is given on the right of the month in the following list: January 11 February 12 March 1 April 2 May 3 June 4 July 5 August 6 September 7 October 8 November 9 December 10. The algorithm enables

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1650-941: Is only necessary to evaluate the terms to the left of the fifth + sign. When calculating the length of any other month it is only necessary to evaluate the terms to the left of the third - sign. d = 30 + ⌊ 0.6 m + 0.4 ⌋ − ⌊ 0.6 m − 0.2 ⌋ − 2 ⌊ m / 12 ⌋ + ⌊ m / 12 ⌋ ⌊ y − 1 4 − ⌊ y − 1 4 ⌋ + 0.25 ⌋ {\displaystyle d=30+\left\lfloor {0.6m+0.4}\right\rfloor -\left\lfloor {0.6m-0.2}\right\rfloor -2\left\lfloor {m/12}\right\rfloor +\left\lfloor {m/12}\right\rfloor \left\lfloor {{\frac {y-1}{4}}-\left\lfloor {\frac {y-1}{4}}\right\rfloor +0.25}\right\rfloor } To find

1725-433: Is rather a kind of mechanical computer making automatic Easter calculations based on ecclesiastical indications at the beginning of a given year. The first computus clock with a fully automatic action was made by the French clockmaker and inventor Jean-Baptiste Schwilgué , the author of the third astronomical clock of Strasbourg Cathedral ( Strasbourg astronomical clock ), between 1838 and 1843. In 1816 he invented and built

1800-402: Is set on the tellurium dial, and its adjustment to correct the dates should be made manually. The computus module has 6 ecclesiastical functions – the 28-year solar cycle, the Gregorian epact, the Gregorian dominical letter, the golden number, the indiction and the indication of the day of the week of January 1 of the next year, so the computation of the Easter date may be provided with the help of

1875-433: Is sometimes supposed. The moon - not necessarily full - can sometimes appear blue due to atmospheric emissions from large forest fires or volcanoes, though the phenomenon is rare and unpredictable (hence the saying “once in a blue moon”). A calendrical blue moon (by Pruett's definition) is predictable and relatively common, happening 7 times in every 19 years (i.e. once every 2 or 3 years). Calendrical blue moons occur because

1950-486: Is the cause of “that epitome of rare occurrences, the blue Moon (seen when forest fires produce clouds composed of small droplets of organic compounds).” A Royal Society report on the 1883 Krakatoa eruption gave a detailed account of “blue, green, and other coloured appearances of the sun and moon” seen in many places for months afterwards.. The report mentioned that in February 1884 an observer in central America saw

2025-421: Is to use the astronomical seasons, which are of unequal length. There is also reference in modern popular astrology to “zodiacal blue moons”. The table below has blue moon dates and times ( UTC ) calculated according to Pruett’s “calendar” rule (second full moon in a calendar month) and two versions of the “seasonal” rule (third full moon in a season with four). The Maine rule uses equal-length seasons defined by

2100-599: The Maine Farmers' Almanac used the term in a slightly different sense from the one now in common use. According to the OED, “Earlier occurrences of the sense given in the Maine Farmers' Almanac have not been traced, either in editions of the Almanac prior to 1937, or elsewhere; the source of this application of the term (if it is not a coinage by the editor, H. P. Trefethen) is unclear.” The conjecture of editorial invention

2175-461: The moon being made of cheese . There is nothing to connect it with the later metaphorical or calendrical meanings of “blue moon”. However, a confusion of belewe (Middle English, “blue”) with belǽwan (Old English “to betray”)) led to a false etymology for the calendrical term that remains widely circulated, despite its originator having acknowledged it as groundless. Percy Bysshe Shelley’s poem "Alastor" (1816) mentioned an erupting volcano and

2250-427: The time between successive full moons (approximately 29.5 days) is shorter than the average calendar month. They are of no astronomical or historical significance, and are not a product of actual lunisolar timekeeping or intercalation . A 1528 satire, Rede Me and Be Nott Wrothe , contained the lines, “Yf they saye the mone is belewe / We must beleve that it is true.” The intended sense was of an absurd belief, like

2325-401: The 3 types appearing. One lunation (an average lunar cycle) is 29.53  days . There are about 365.24 days in a tropical year . Therefore, about 12.37 lunations (365.24 days divided by 29.53 days) occur in a tropical year. So the date of the full moon falls back by nearly one day every calendar month on average. Each calendar year contains roughly 11 days more than

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2400-547: The D.G.Burylin Museum, Ivanovo, Russia). The French clockmaker Paul Pouvillon included a computus module in his complicated astronomical clock with orrery, made from 1918 to at least 1939 (and probably into the 1960s). The module has a single indicator of the Gregorian Easter date in a window with a disc underneath, stamped with the Easter dates for the 19-year period from 1946 to 1964. The moveable feast's indicator

2475-503: The Easter date for the Julian calendar. The indication of the date of the upcoming Easter is one of the rarest astronomical functions of mechanical clocks and watches due to the high levels of complexity involved. Moreover, there is significant discrepancy in computus algorithms due to the differences of the Julian and Gregorian calendars ( Easter controversy ). The obvious difficulties in implementing computus algorithms in clockwork explain

2550-471: The Easter date for themselves forced attempts to establish clear rules for the Easter date calculation and finally the algorithms for this. The determination of the Easter date requires calculating astronomical and calendar cycles – the annual motion of the Sun round the celestial sphere, the evolution of the phases of the Moon, the cycle of the days of the week, particularities of calendars and some agreements like

2625-469: The French clockmaker Auguste-Lucien Vérité from 1865 to 1868. The cam wheel is calculated for a period of 300 years, and the computus also has dials for indications of the dominical letter, the epact, the 28-year solar cycle, the golden number and the indiction. Separated computus module is produced to demonstrate the principal action of a computus device of a clock, to try and check the complicated mechanism. Separated modules are quite remarkable because just

2700-478: The Maine rule is sometimes called the “seasonal”, “true” or “traditional” rule (though of course no tradition of it exists prior to 1937). Blue moons by Pruett’s definition are sometimes called “calendar blue moons”. The "seasonal" blue moon rule is itself ambiguous since it depends which definition of season is used. The Maine rule used seasons of equal length with the ecclesiastical equinox (March 21). An alternative

2775-478: The Vulgar Tongue’’, edited by Egan, included the definition: “Blue moon. In allusion to a long time before such a circumstance happens. ‘O yes, in a blue moon.’” An earlier (1811) version of the same dictionary had not included the phrase, so it was likely coined some time in the 1810s. "Once in a blue moon" is recorded from 1833. The use of blue moon to mean a specific calendrical event dates from 1937, when

2850-448: The almanac in the U.S. magazine Sky & Telescope (July 1943, page 17) in answer to a reader’s question about the meaning of “blue moon”. Then James Hugh Pruett (1886-1955) quoted it again in Sky & Telescope (March 1946, p3), saying “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

2925-436: The calendrical definition of “blue moon” that is now most commonly used, i.e. the second full moon in a calendar month. “A blue moon in the original Maine Farmers' Almanac sense can only occur in the months of February, May, August, and November. In the later sense, one can occur in any month except February." This later sense gained currency from its use in a United States radio programme, StarDate on January 31, 1980 and in

3000-455: The children’s book), and in 1988 a forthcoming blue moon received widespread press coverage. In 1999 U.S. astronomer Donald W. Olson researched the original articles and published the results in a Sky & Telescope article co-authored with Richard T Fienberg and Roger W. Sinnott. From the examples given by Trefethen in the 1937 Maine Farmers’ Almanac they deduced a “rule” he must effectively have used. “Seasonal Moon names are assigned near

3075-400: The computus mechanism consists of more than 300 parts. The Orthodox computus has been used in a series of Chaykin's astronomical desk clocks – the “Resurrection Computus Clock” (2007), the “Northern Computus Clock” (2015) and the supercomplicated “Moscow Computus Clock” (2016). This type of computus mechanism does not provide a mechanical calculation of the Easter date, but shows it by means of

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3150-934: The crescent moon as “a magnificent emerald-green” while its ashen part was “pale green”. Venus, bright stars and a comet were also green. The report authors suspected that green moons were a contrast effect, since in those cases the surrounding sky was seen as red. People saw blue moons in 1983 after the eruption of the El Chichón volcano in Mexico, and there are reports of blue moons caused by Mount St. Helens in 1980 and Mount Pinatubo in 1991. The moon looked blue after forest fires in Sweden and Canada in 1950 and 1951, On September 23, 1950, several muskeg fires that had been smoldering for several years in Alberta, Canada, suddenly blew up into major—and very smoky—fires. Winds carried

3225-617: The date of the Christian festival of Easter depended on an accurate computation of full moon dates, and important work was done by the monks Dionysius Exiguus and Bede , explained by the latter in The Reckoning of Time , written c725 CE. According to Bede, “Whenever it was a common year, [the Anglo-Saxons] gave three lunar months to each season. When an embolismic year occurred (that is, one of 13 lunar months) they assigned

3300-473: The date of the so-called ecclesiastical equinox., designated as March 21, irrespective of the actual astronomical observation by the Church of Alexandria in the beginning of the 4th Century. Specific astronomical data which may be incorrect, misinterpreted or location dependent, were eliminated from the Easter date calculation by the invention of special paschal functions – “letters” and “numbers”. They include

3375-474: The dates of Easter since 1583. The Gregorian computus was later adopted by most Protestant churches – between 1753 and 1845 – while most Eastern Churches, including the majority of Eastern Orthodox Churches and Non-Chalcedonian Churches continued to produce the Easter date computation based on the Julian calendar (Alexandrian computus), although both had and indeed still have some complications, described in detail in dedicated studies. The Alexandrian computus gives

3450-524: The design and construction were described in detail by Dondi in his manuscripts and provided enough material for modern clockmakers to build reconstructions. While few reconstructions have been made, one example of Dondi's computus can be found in the Smithsonian Institution (Washington DC, USA). Dondi's computus was based on a device with a wheel drive and three chain indicators of the 7980-year Julian period. The first chain with 28 links

3525-420: The dominical letter, the epact, the 28-year solar cycle, the golden number and the indiction was made by the French clockmaker Auguste-Lucien Vérité in his monumental astronomical pendulum clock of Besançon Cathedral (France). Built from 1858 to 1860, the clock's epact dial has an additional indication of Easter dates for a period of 19 years on cartouches, which should be replaced or repainted every 19 years by

3600-565: The dynamical mean sun, and is presumed to have been the original rule of Trefethen. The “astro-seasonal” rule uses the unequal astronomical seasons defined by the apparent sun. All calculations are by David Harper. The fourth column shows blue moon dates that were actually printed in the Maine Farmers’ Almanac , as found by Olson, Fienberg and Sinnott in 1999. They studied issues published between 1819 and 1962, and found that all mentions occurred between 1937, when H.P. Trefethen introduced

3675-502: The ecclesiastical functions even for the years after 1964, when the original Easter date disc is no more valid, as noted during restoration works in 2011–2012. Indications of the 28-year solar cycle, golden number and indiction were used by the Norwegian clockmaker and inventor Rasmus Jonassen Sørnes in his complicated astronomical pendulum clock No.4 (Sørnes No.4), built from 1958 to 1966. The most complicated type of computus clock

3750-402: The expression "Once in a Blue Moon". There is no evidence that an extra moon in a month, season or year was considered unlucky, or that it led to 13 being considered unlucky , or that the extra moon was called "blue", or that it led to the phrase "once in a blue moon". There is good reason to suspect that the 1937 article was a hoax, practical joke, or simply misinformed. It is however true that

3825-412: The extra month to summer, so that three months together bore the name ‘‘Litha’’; hence they called [the embolismic] year ‘‘Thrilithi’’. It had four summer months, with the usual three for the other seasons.” The name Litha is now applied by some Neo-Pagans to midsummer . The 1937 Maine Farmers' Almanac article was misinterpreted by James Hugh Pruett in a 1946 Sky and Telescope article , leading to

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3900-399: The fact that in the entire history of mechanical clocks and watchmaking, just a few examples of computus clocks and watches have been made. Clocks with a tabular computus provide the indication of special paschal (ecclesiastical) functions without the automatic counting of the date of Easter, so the date should be determined by the paschal table with the use of indications - the golden number,

3975-411: The fact that the duration of the period is 5,700,000 years (70,499,183 lunar months or 2,081,882,250 days). The German mathematician Karl Gauss presented a computus algorithm in 1800 and finalized it in 1807 and 1811. Gauss’ algorithm is considered to be the most commonly used and although it was intended for calculating the Easter date for the Gregorian calendar, it is also valid for the calculation of

4050-617: The first computus clock of this type invented and made by Russian watch- and clockmaker Konstantin Chaykin. A mechanical Orthodox computus was developed by Konstantin Chaykin using a novel computus algorithm, that differs from Carl Friedrich Gauss's algorithm. The computus mechanism mechanically calculates the Orthodox Easter date at midnight at New Year and sets the calendar for the following year by means of three cam wheels, springs, levers, racks and three differential gears. In total,

4125-419: The first prototype of his mechanical computus “Comput ecclésiastique”, and in 1821 he made the final calculations and design of his device, acting as a Gregorian computus. Schwilgué embedded his computus into the astronomical clock of Strasbourg Cathedral, where it continues to operate to this day. It includes 5 ecclesiastical functions – the 28-year solar cycle, the Gregorian epact, the Gregorian dominical letter,

4200-470: The golden number and the indiction, with the addition of a 4-digit Gregorian year indicator. At the start of each year, the computus changes the indications of the dates of Easter and moveable feasts on the annual calendar ring of the main dial in the central lower part of the clock. The Danish clockmaker Jens Olsen , while visiting Strasbourg in 1897, was inspired by Jean-Baptiste Schwilgué's astronomical clock of Strasbourg Cathedral and in 1924 he completed

4275-439: The integral or floor function: thus ⌊ x ⌋ {\displaystyle \left\lfloor {x}\right\rfloor } is that part of the number x which lies to the left of the decimal point. It is only necessary to work through the complete function when calculating the length of February in a year which is divisible by 100 without remainder. When calculating the length of February in any other year it

4350-553: The keeper of the clock. Ecclesiastical functions of the 28-year solar cycle, the Julian epact, the Gregorian epact, the Julian dominical letter, the Gregorian dominical letter, the golden number and the indiction were implemented by the Swiss watchmaker Albert Billeter in his supercomplicated monumental “Ivanovo” Universal Clock, which he made in 1873 in Paris and which is kept in Ivanovo Museum of Industry and Arts (also known as

4425-1307: The length of, for example, February 2000 the calculation is + ⌊ ⌊ 0.3 + 20 − 3 4.5 − ⌊ 20 − 3 4.5 ⌋ ⌋ + 99 100 ⌋ − 1 {\displaystyle +\left\lfloor {\cfrac {\left\lfloor {0.3+{\cfrac {20-3}{4.5}}-\left\lfloor {\cfrac {20-3}{4.5}}\right\rfloor }\right\rfloor +99}{100}}\right\rfloor -1} = 30 + 7 − 7 − 2 + ⌊ 499.75 − 499 + 0.25 ⌋ + ⌊ ⌊ 0.3 + 3.77 − 3 ⌋ + 99 100 ⌋ − 1 {\displaystyle =30+7-7-2+\left\lfloor {499.75-499+0.25}\right\rfloor +\left\lfloor {\frac {\left\lfloor {0.3+3.77-3}\right\rfloor +99}{100}}\right\rfloor -1} = 28 + 1 + 1 − 1 {\displaystyle =28+1+1-1} = 29. {\displaystyle =29.} Calendrical Calculations This applied mathematics –related article

4500-511: The metaphorical one, and inspired various folk etymologies , e.g. the “betrayer” speculation mentioned earlier, or that it came from a printing convention in calendars or a saying in Czech. A 1997 Taiwanese movie, Blue Moon , had the log line “There is usually only one full moon every month, but occasionally there are two – and that second full moon is called the Blue Moon. It is said that when

4575-453: The moon turn red; thus red moons are far more common than blue moons. Blue moon as a calendrical term originated with the 1937 Maine Farmers’ Almanac , a provincial U.S. magazine that is not to be confused with the Farmers' Almanac , Old Farmer's Almanac , or other American almanacs . There is no evidence of “blue moon” having been used as a specific calendrical term before 1937, and it

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4650-459: The number of days in 12 lunar cycles, so every two or three years (seven times in the 19 year Metonic cycle ), there is an extra full moon in the year. The extra full moon necessarily falls in one of the four seasons (however defined), giving that season four full moons instead of the usual three. 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

4725-460: The overlapping frequencies of these 3 rules), it so happens there are not any 2 sequential years (at least within these 200) wherein none of the 3 types of blue moon occur. Conversely, despite the preponderance of years with blue moons (of at least 1 type) occurring in this 200-year range, there are no instances of more than 4 sequential years having a blue moon, of any of these 3 types -- i.e. at least 1 year out of every 5 sequential years has none of

4800-441: The regular arrangement of church festivals. For this reason thirteen came to be considered an unlucky number. Also, this extra moon had a way of coming in each of the seasons so that it could not be given a name appropriate to the time of year like the other moons. It was usually called the Blue Moon... In olden times the almanac makers had much difficulty calculating the occurrence of the Blue Moon and this uncertainty gave rise to

4875-692: 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 1   micrometre in 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. Ice particles might have

4950-482: The solar cycle, the epact, the dominical letter, and the indiction – all or some of which, may be with the addition of other indications. It is believed the first Easter function in a mechanical clock was created by the Italian physician, astronomer and mechanical engineer Giovanni Dondi dell'Orologio from Padua. He built his complicated astronomical clock “ Astrarium ” from 1348 to 1364. The clock has not survived, but

5025-440: The spring equinox in accordance with the ecclesiastical rules for determining the dates of Easter and Lent . The beginnings of summer, fall, and winter are determined by the dynamical mean Sun . When a season contains four full Moons, the third is called a Blue Moon.” They termed this the “Maine rule” for blue moons, as distinct from Pruett’s 1946 definition that was seen to have been a misinterpretation. In popular astronomy

5100-513: The term, and 1956, when Trefethen’s editorship ended (consistent with it being Trefethen’s own invention). Occasional discrepancies between the Maine rule and the almanac’s printed dates can be ascribed to clerical errors or miscalculation. In one case (August 1945) Trefethen appears to have used the apparent rather than mean sun. The table shows that in 200 years there are 187 full moons that could be called "blue" by some definition - an average of nearly one per year. Two Pruett blue moons can occur in

5175-575: The tradition that Easter Sunday is the first Sunday after the first full moon (Paschal or ecclesiastical full moon ) on or after the spring equinox (21 March), and Easter Sunday should not occur on the same day as the Jewish calendar date Nisan 15th, the first day of Passover week. In early Christianity, the Easter date was calculated each year and announced by the Pope. The later need for Christian clergy living in different territories to be able to calculate

5250-402: The works of Jean-Baptiste Schwilgué and his astronomical clock of Strasbourg Cathedral. Vachey spent thirty years – from 1938 to 1968 – building his supercomplicated astronomical computus clock. The computus of the clock has 5 ecclesiastical functions – the Gregorian dominical letter, the Gregorian epact, the 28-year solar cycle, the indiction and the golden number. The clock is also equipped with

5325-419: The “ golden number ” (which gives the dates of all the new moons for the year in a 19-year Metonic cycle), the solar cycle (the 28-year cycle of the Julian calendar and 400-year cycle of the Gregorian calendar with respect to the week), the epact (the age of the Moon in days on a certain date), the dominical letter (used to determine the day of the week for particular dates) and the indiction (the number of

5400-593: The “Calibre 89” and one functioning prototype were made in 1989 (the prototype is stored in the Patek Philippe Museum in Geneva, Switzerland). The Easter date display uses a program cam wheel valid for 28 years. It is assumed that this will be replaced as each term for its correct operation expires. An extended program cam wheel mechanism was used in the display of the Easter date in the monumental astronomical clock of Beauvais Cathedral (France), built by

5475-416: Was possibly invented by the magazine’s editor, Henry Porter Trefethen (1887-1957). As a term for the second full moon in a calendar month it began to be widely known in the U.S. in the mid-1980s and became internationally known in the late 1990s when calendrical matters were of special interest given the approaching millennium. It created a misapprehension that the calendrical meaning of “blue moon” had preceded

5550-539: Was proposed in 725 by the English Benedictine monk Bede in his treatise “De temporum ratione” (“The Reckoning of Time”). Alexandrian computus, based on rules established by the Church of Alexandria, was universally used from the beginning of the 8th century until the Gregorian calendar reform of 1582. The Roman Catholic Church has used the Gregorian calendar, and accordingly Gregorian computus, to calculate

5625-414: Was used to indicate the dominical letter and the 28-year solar cycle, the second chain with 19 links was used to indicate the golden number, and the third chain was used for the 15-year cycle of indiction. The computus was set under the date display ring, which was designed for a 365-day year (in the leap year, Giovanni de Dondi intended to stop the clock for one day). A tabular computus with indications of

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