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Ecclesiastical Calendar: Enter a Year...Named a MAGELLAN 3 STAR SITE on1996 January 20.Named a POINT TOP 5% SITE on 1996 February 27. 1997 July 5Named Links2Go#2 in Calendars Topic on 1999 October 1. Calculation of theEcclesiastical CalendarResources and Acknowledgements |Links to this page |Related Links |DISCLAIMERPlease enter a year after A.D. 325 (see text below).Ecclesiastical Calendar for which year: A.D. Orthodox - New CalendaristsOrthodox - Old CalendaristsWesternHere is a list of Orthodox Easter dates listed in the Julian Calendar or the Gregorian Calendar, 1875-2124.Here is a list of Western Easter dates AD1875-2124.Here is a list of years with the same Julian date or Gregorian date of Orthodox Easter, AD 1875-2124. Here is a list of years with the same date ofWestern Easter, AD 1875-2124.Here is a Table of the frequency of the difference between the dates of Orthodox and Western Easter, AD 1583 toAD 3000.IntroductionThis program calculates:Easter Sunday in boththe Western (Catholic, Anglican, and Protestant) Christian, andin the Eastern (Orthodox) Christian traditions;The movable Feasts associated with Easter in the Westernand Eastern traditions;Many Feasts in the Catholic calendar, usually celebrations of events in the lives of Jesus or Mary. (These Feasts may or may not be celebrated by other Christian denominations.)For years before 1583, only the dates of Christmas and Easter are calculated. (They are the same for both traditions pre-1583.)My recent research (email and bookwork)has shown that the above method for calculating Easter prior to AD1583 was not in wide usageuntil the mid-eighth century, although it had been adopted by the Church in themid-sixth century.An important note for historians and people using thesedates for research: Even though the Gregorian calendar wasadopted intouse by the Catholic Church and many Catholic areas of Europe in AD 1582October, many areas did not adopt the Gregorian Calendar, the new method of determiningEaster, or both, until later. A good review is given in reference (1). For example, England and its dominions did notaccept the Gregorian Calendar or the new method of determining Easteruntil 1752; thus, Easter in England prior to 1753 was determined usingthe same algorithm as that of the Orthodox Church. I have summarized some information on the Orthodox Ecclesiastical Calendarand an algorithm by Gauss to calculate the date of the Orthodox Easter.Easter CalculationsHistoryPrior to AD325, churches in different regions celebrated Easter on differentdates, not always on Sundays.The Council of Nicea (AD 325) clarified this a bit by stating that Easter wouldbe celebrated on Sundays. Still a number of methods were used until a methoddefined by Dionyisius Exiguus was adopted in about AD 532.This was not widely accepted until it was described and defended by the Venerable Bede in his De temporum ratione(AD 725). [Thanks to Jim Morrison(70451.2106@compuserve.com) for the previous four sentences.]Aloisius Lilius (d. 1576) devised the system thatwould become the basis of the Gregorian Calendar, as well as thetables that would be used to determine the date of Easter.Christoph Clavius modified the tables slightly, andwas one of the prime defenders of the Gregorian calendar. The tablesused to determine the date of Easter (in the West) since AD 1583 arethese modified tables of Clavius. All algorithms for calculating thedate of Easter since then are based on these tables.Easter is the Sunday after the Paschal Full Moon. ThePaschal Full Moon may occur from March 21 through April 18, inclusive.Thus the date of Easter is from March 22 through April 25, inclusive.The date of the Paschal full moon is determined from tables, and it maydiffer from the date of the the actual full moon by up to two days.This definition, along with tables, etc. may be found in "TheExplanatory Supplement to the Astronomical Ephemeris and AmericanEphemeris and Nautical Almanac". This definition that uses tablesinstead of actual observations of the full moon is useful and necessarysince the the full moon may occur on different (local, notUT) dates depending where you are in the world. If the date of Easterwas based on local observations, then it would be possible fordifferent parts of the world to celebrate Easter on different dates inthe same year. To further confuse the issue, many countries did not start using the Gregorian calendar in October 1582, so Easter in those countries was celebrated at times different than is listed here UNTIL they began using the Gregorian calendar. And some countries that switched to the Gregorian calendar used a differentdefinition of Easter for some time (parts of Germany and Sweden usedtables based on the observations of Tycho Brahe to determine Easter for many years after the Gregorian calendar was adopted in those locations).A reasonably comprehensive list of when nations started to use the Gregorian Calendar may be found in reference (1) and in the Calendar FAQ.An interesting upshot of the algorithm is that thecycle of Easter dates (in the Gregorian Calendar) repeats every5,700,000 years - and no sooner! (See the CalendarFAQ for why the period has this particular length.) Using thealgorithms, I have calculated the distribution of the Gregorian Easterdates over various periods of time. You may view the frequency of thedate of Easter over one complete 5,700,000 yearcycle, or over the first complete 400 year Gregorian Calendar cycle, or over a more contemporary timespan of1875 to 2124.AlgorithmsThe algorithm used to calculatethe date of Easter in the Western tradition (after 1582) isfrom Practical Astronomy with your Calculator by PeterDuffett-Smith and he got it from "Butcher's Ecclesiastical Calendar"(1876); apparently the algorithm was first published anonomously in Nature in 1876. This particular algorithm uses just integer math. The algorithm is valid for all yearsin the Gregorian calendar, that is October 1582 and onwards. Carter's algorithm is a more simple method forcalculating the date of Easter and it is valid only from 1900 until 2099.Doggett's modification of Oudin's algorithm iseasy to use and is valid after AD 1583. Mallen'smethod is another general, easy to use method.Some published methods do not for work for all years, and the method at this link from the 11th Edition Encyclopedia Brittanica unfortunatelyfails in some cases.There is a useful collection of articles gleaned from thesoc.religion.christian newsgroupdiscussions that contains some history, as well as explanation of thealgorithms used by both the Orthodox and Western churches that hasbeen collected as an Easter-DateFAQ; it has both some C code and an amazing Bourne shell scriptfor calculating the date of Easter.Finally, there is asimple algorithmdue to Gauss for calculating the date of the Orthodox Easter.A few other useful algorithms are also listed on my American Secular Holidays Page. This includesalgorithms for determining dates such as "The Second Sunday in May".Future Validity of All Algorithms of Determining the Date of EasterThere are many reasons to expect that all methods of determining thedate of Easter will not be valid in the far future. The prime physicalreason is that the length of the day is increasing, thus the number ofdays in a year is slowly decreasing. The current rate of increase inthe length of the day implies that the Gregorian calendar will need toneglect a leap year sometime in the 4th or 5th millenium.A greater likelihood is that some time in the near future the date ofEaster may be fixed to a particular Sunday. At Vatican II, Pope JohnXXIII stated that there was nothing wrong with fixing the date ofEaster. And there seems to be broad support in the World Council ofChurches for a fixed celebration of Easter. According to theEncyclopaedeia Brittanica, the second Sunday in April isthe most favored date. Fixing the date of Easter to a particularSunday would still mean that Easter and the Feasts related to it wouldbe movable, but the movement would be restricted to a span of sevendates (for example, the second Sunday in April must fall between April8th-14th). Most of the discussion on this issue appears to havehappened in the 1960's-1970's, but there is a press release from the Aleppo meeting of the World Council of Churches that discusses new proposals for fixing the date of Easter for all ofChrisitianity. The press release is dated 1997 March 24, and the basicsuggestion is to use astronomical measurements of the vernalequinox and the full moon at the meridian of Jerusalem in order todetermine the date of Easter. The authors of the proposal wantedthis method to be adopted in the year 2001. Currently no Church hasadopted this proposal. Please visit William Morris' New Easter Dateswebsite for a comparison of Easter dates in the Gregorian and OrthodoxCalendars, along withdates calculated using the Aleppo proposal,and dates calculated as the Sunday after Passover. Feasts Related to EasterOf interest from the reference (1)(which is a pre-Vatican II source!) are the following dates, and theirrelation to Easter. Days Before Easter Days after EasterSeptuagesima 63 Rogation Sunday 35Quinquagesima 49 Ascension 39Ash Wednesday 46 Pentecost 49Palm Sunday 7 Trinity Sunday 56Good Friday 2 Corpus Christi 60Matthew Bear (mtbear@mit.edu) was the first to inform me that Septuagesima, and Quinquagesima were in a pre-Lent seasonprior to Vatican II (in the Catholic church) or the 1970's (various Protestantdenominations); Rogation Sunday was the Sunday before the Rogation (prayer, supplication) days before Ascension.Alex Kochergin writes that in the Eastern Orthodox perspective, Septuagesima and Quinquagesima are still celebrated- in fact, the three Sundays of Pre-Lent before Lent starts have as their Gospel Readings: the Parable of the Publican and the Pharisee, the Parable of the Prodigal Son, and Christ's reminder of the Last Judgement.Celebrations in the Ecclesiastical CalendarNot Related to EasterOnce we have determined a date of the year and a day of the week,we can fix each date of the year to a day of the week. While my algorithmuses Easter to do this, general algorithms exist that allow the determinationof the day of the week for a particular year (see theCalendar FAQ).Sundays in Advent are determined in the following straightforwardmethod. First, the feast of Christ the King is the Sunday on or after20 November; the First Sunday of Advent is the Sunday on or after 27 Nov.;the Second Sunday of Advent is on or after 4 Dec.; the 3rd Sunday of Advent is on or after 11 Dec.; finally, the 4th Sunday of Advent is on or after 18 Dec. The day of the week that Christmasfalls on can then be easily determined. Other Feasts that are listed by the Ecclesiastical Calendar are:The Solemnity of Mary on 1 January;Epiphany on 6 January (traditional) or the 2nd Sundayafter Christmas;The Presentation of the Lord on 2 February;The Annunciation usually on 25 March;The Transfiguration of the Lord on 6 August;The Assumption of Mary on 15 August;The Birth of Virgin Mary on 8 September;The Celebration of the Holy Cross on 14 September;The Mass of the Archangels on 29 September;and All Saints' and All Souls' on 1 November and 2 November, respectively.I still have limited the determination of these feaststo dates in the Gregorian Calendar. It is not impossible to calculate feasts for dates before then - I just have not done it. In addition, until recently some of the celebrations I list may not have been standard, defined, or celebrated on the dates currently listed. (In particular,some of the celebrations may have been celebrated on different dates before Vatican II). Resources, Acknowledgements, and Further Reading"The Explanatory Supplement to the AstronomicalEphemeris and American Ephemeris and Nautical Almanac" (1961, Her Majesty's Stationery Office [QB8.G82.1962]) has tables for calculating Easter, as well as the dates various countries/regions adopted theGregorian calendar, and other very useful information on calendars and ephemerides. Many of the relevant sections may be found at Calendars and theirHistory. The Calendar FAQby Claus Tonderinganswers many questions concerning calendars, leap years, the Christian, Hebrew,and Islamic calendars. Check this out if you want to find the algorithmfor making a Hebrew calendar.The Easter-DateFAQ has useful historical and algorithmic information on how thedate of Easter is determined."Practical Astronomy with your Calculator" (2nd Edition, 1981, Cambridge University Press) by Peter Duffett-Smith has many useful algorithms,including the calculation of the date of Easter in the Gregorian Calendarthat I use."Butcher's Ecclesiastical Calendar" (1867) is the original sourceof the algorithm that I use. "The Gregorian Calendar" (1982 May, Scientific American, Vol. 246, No.5, p 144) by Gordon Moyer is a very good review about the adoption of the Gregorian Calendar.Special thanks to Matthew Bear (mtbear@mit.edu) who provided many useful comments within a week after the page was publicly advertised. I have made some changes basedon information he has provided, but I have not had the time to make all thechanges. Special thanks also toAlex Kochergin who provided me with pretty much ALL the information here regarding thedates and celebrations in the Eastern Orthodox Church.A note about different calendars: dates in the Hebrew, Islamic, Julian,ISO, Mayan, French Revolutionary and Julian (astronomical) date calendar, as well as their correspondence to dates in the Gregorian calendar may be found using the "calendar" mode in the Free Software Foundation's GNU Emacs (at least since version 19.28.1 - it may have been available in earlier versions, too). To get to calendar mode in these versions of Emacs, use the sequence "Meta-x calendar". This will keep you occupied if you enjoy calendars.Calendrical Calculations, a very useful book by Dershowitz & Reingold.An almanac that has a list of Easter dates through 2100 is theWorld Almanac (Mahwah, NJ: Funk and Wagnalls, 1994). I suspect otheralmanacs also have tables like this - I have not read all of them.This form was made using routines from the cgi-lib.pl packageby Steven E. Brenner.Folks providing links to this page (incomplete)This list is extremely incomplete and seriously out of date. Many peoplehave links to my pages now, and it would take up an inordinate amount ofspace to list all of them.I keep this section since it lists the first folksthat I know about that provided links to this hierarchy of pages.Thanks to everyone who provides links to this page. Geraint Jennings Yahoo Galaxy Directory Services St. Columbia Press, anexcellent resource for information about the Orthodox Church Linksto this page according to AltaVista Related Links William Morris' New Easter Dates, with dates calculated using the propsed Aleppo formula. Dave Goode's Orthodox EcclesiasticalCalculator using Javascript The Royal GreenwichObservatory's Leafletson the Date of Easter,the Calendar, andLeap Years How Easter Date is determined, an excellent, clear and colorful presentation on determining the date of Easter, along with Mallen's algorithm. Henk Reints' Collection of Easter Algorithms ASimplified Easter Dating Method by R.W. Mallen, Adelaide, Australia A Calendar of Jewish Feasts by B'nai B'rith Andrew McNab's Perpetual Calendar Form Festivalsand HolidaysToday's Calendarand Clock Page has links to information and calendars from many differenttypes, including (but not limited to) Jewish, Islamic, and Chinese.Kalendar for Todaygives information about readings and what feast or celebration might be today.The Catholic CalendarPage has beautiful and informative calendars for the current year.TheCalendar FAQ, by ClausTondering is an excellent resource.The World Wide Holidayand Festival Page by Brian Prescott-Decie contains links to pageswith both religioious and secular holidays.Easter,Rosh Hashanah, and Passover by William H. JefferysThe Date ofEaster from the Anglican Diocese of ElyDatesof Ash Wednesday and Easter Sunday and The Date ofEaster from the AstronomicalApplication Dept. of the U.S. Naval ObservatoryThe Liturgy of the HoursGeneral RomanCalendar of Feasts, Solemnities, and MemorialsKenneth Bath's ROMCALVersion 3, C source code for a program to generate a RomanCatholic Calendar, including support for generating color PostScriptand HTML calendars.If you liked this page, please visit my American Secular Holidays Page.DisclaimerThe views and writings presented here are my own,and are NOT the responsibility of Smart Net.I have consulted many sources, and I believe that the work I havepresented is correct. However, since sometimes hardware and/or softwaremisbehave in subtle ways, and since I may, on occassion, mistype, oreven accidentally use wrong or mistaken sources, the followingdisclaimer applies to all the pages in this hierarchy: IFYOU ARE USING THESE DATES TO PLAN TRAVEL, MEETINGS, OR FOR ANY USEREQUIRING THE EXPENDITURE OF MONEY, TIME, OR OTHER RESOURCES, PLEASECONSULT OTHER SOURCES TO VERIFY THE DATES OF THE VARIOUS HOLIDAYS.Neither Marcos Montes nor anyone who owns the hardware or manages thehost machines of this home page, nor anyone who has contributed anyinformation that I have used on these pages, may be held financiallyresponsible, or responsible in any way, if these dates are wrong. Theuser assumes full responsibilty for the consequences of using thisinformation.Top |Resources and Acknowledgements |Some links to this page |Related Links |DISCLAIMERLast updated 2001 July 31.Copyright © 1996-2001 by Marcos J. Montes.Marcos J. MontesMy American Calendar Page.mmontes@no.spam.smart.net |
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