Computus

The Passover is in Christianity celebrated in principle on the first Sunday after the first full moon in spring . For simplicity, however, this is based on a calculated date based on a simplified representation of the movement of the heavenly bodies, in which one uses the Epact . Easter Sunday falls roughly in the middle of the annual easter cycle and determines when the other religious holidays fall within this cycle. As is Ash Wednesday, which the fasting begins, always 46 days before Easter (there are forty days of fasting, Sundays during this period do not count), Ascension always 39 days later, Pentecost always on the 7th Sunday after Easter, the 49th day after Easter or 50th day of Easter (in Ancient Greek : πεντηκοστή (ἡμέρα) pentekostē (Hemera), 50 of which Pentecost is derived).

The dates of the Solemnity of the Holy Trinity ( Sunday after Pentecost ), Corpus Christi (second Thursday after Pentecost), Sacrament Sunday (the second Sunday after Pentecost) and the Solemnity of the Sacred Heart (third Friday after Pentecost) are at the date of Easter connected.

Content

 * 1 History
 * 2 Method of Gauss
 * 3 Differing Easter dates
 * 4 Table with data Easter, Ascension and Pentecost
 * 5 Future developments
 * 6 Trivia
 * 7 Source
 * 8 See also
 * 9 Easter Calculations

History [ edit ]
In the first centuries of the Christian church fourth Easter on the same day as the Jewish Passover (Nisan 14), but the Council of Nicaea in 325 wanted to proceed to an independent calculation of the date of Easter.The rules of this council are based on a simplified calculation of the average positions of the sun and moon (circular orbits and fixed speed) and 21 March 0:00 am as solid beginning of spring. The true moon today differs to ± 0.7 day on the average moon, and the astronomical beginning of spring (see vernal equinox ) eg varies between March 19 9:00 (CET) in the year 2096 and 21 March 21:00 ( CET) in the year 1903. Thus sometimes be differences between the ecclesiastical and the astronomical date of Easter ("paasparadoxiën").

Initially, the rules were applied in different ways. For example, fourth in 387 Rome on 21 March Easter, Alexandria on 25 April and other churches on 18 April. The Scythian monk Dionysius Exiguus suggested in the year 525 in Rome tables and an algorithm according to the Alexandrian rules. He applied the calculation so that Easter at the earliest on 22 March and by 25 April falls. The Pope now decided to celebrate Easter according to these rules and tables and transfer determining the date of Easter to the patriarch (bishop) of Alexandria.

Since the year 532 (the beginning of the Easter tables of Dionysius Exiguus) the dates are fixed, but only in the 9th century, the so calculated Easter dates generally accepted by Christians . In the Middle Ages, however, they noticed that the calculated Easter dates noticeably began to deviate from the celestial phenomena. As the beginning of astronomical spring still fell earlier in the 16th century, this already postponed until March 11. The deadline for the ecclesiastical full moon was three days differ from the astronomical full moon. During that time they used the Julian calendar by Julius Caesar introduced in the year 46 BC, in which one strictly one to four years leap entered.

The introduction of the Gregorian calendar by Pope Gregory XIII in 1582 had to offer a solution to these problems. First was allowed ten days away, so the beginning of astronomical spring weather was around 21 March. A small change in the schrikkeljaarregeling had to make sure that this was so in the future. For the calculation of the ecclesiastical full moon was one by the Italian astronomer Aloysius Lilius implemented proposed improvement of the rules, so that it would remain on average in line with the astronomical full moon. By lunging leap years there was no simple relation between the more golden number and Epact and the 8 extra Mondays per 2500 years were further adjustments nodig.Bovendien he was not too much different from the previous calculations because otherwise the reputation of earlier philosophers (and the church) would harm. A committee chaired by Christopher Clavius ​​(which include Niklaus Koppernigk ( Copernicus ) and Aloysius Lilius took place) has then been proposed a fixed date of Easter, but it was rejected because it was too big a break with the past. There were also some trifling differences by Christopher Clavius ​​calculated Easter moon and the real moon, so there was an on Easter Sunday 1903 lunar eclipse . Furthermore, was already known that there is a southern hemisphere was, so it was claimed that because Jesus on the northern hemisphere had lived, the people in the southern hemisphere had to abide by the northern spring .

[Method of Gauss edit ]
The German scholar Carl Friedrich Gauss published in 1800 a mathematical algorithm the Easter date can be calculated for any given year. Gauss nevertheless made ​​a mistake: he did not properly take into account the moon correction, so that, for example, date of Easter for 4200 comes out on April 13 instead of April 20th. Gauss's method is as follows:
 * 1) Determine the golden number:  Divide the year by 19, take the rest, then add 1 to (like Dionysius ). Call this number G. For the year 1991 G = 16 applies.
 * 2) Determine the eeuwtal:  Part whole the year 100 and add 1 to to this. Call this number C. 1991 C = 20 applies.
 * 3) Then correct for years that no leap year are:  Multiply C with 3 completely divide by 4 and subtract 12 from it. Call this number X. For the twentieth and twenty-first century is X = 3.
 * 4) Moon Correction:  Take 8 times C, count on there at 5, whole part this by 25 and subtract 5 from. Call this number Y. For the twentieth and twenty-first century is: Y = 1.
 * 5) Search Sunday:  Multiply the year with 5 whole part the result by 4, X and subtract 10 from it, and call this number Z. For 1991, the following applies: Z = 2475.
 * 6) Determine the Epact :  11 times 20 + G + X Y. pull it off, completely divide by 30 and call the rest E. If E is equal to 24, or if E is equal to 25 and the golden number is greater than 11, then count 1 at E on. The Epact for 1991 14.
 * 7) Determine the full moon:  Pull E from 44. Call this number N. If N is smaller than 21, please add 30 to that number. 1991: N = 30
 * 8) Now through to Sunday:  Tel Z and N in. Completely Divide the result by 7 and pull the remainder from N + 7. Call this number P. For 1991, the following applies: P = 31.
 * 9) Easter Date : If P is greater than 31, then pull it from 31, and the date of Easter falls in April. Otherwise, the day of Easter P in March. For example, for 1991 found 31 of March.

Differing Easter dates [ edit ]
In many Eastern Orthodox Churches was the old Julian calendar (the Dionysian Easter date calculation) until the 20th century in use. A conference of Eastern Orthodox Churches in Constantinople proposed in 1923 a new church calendar, which until 2800 corresponds to the Gregorian calendar; the date of Easter would be determined on the basis of astronomical observations. The Autocephalous Church of Romania took this calendar and the astronomical date of Easter on. Greece took in 1924 or the calendar, but the Greek Orthodox Church continued to calculate the date for Easter and the simultaneous cycle (not the other holidays) at the Julian calendar. In other Orthodox Churches, the Julian calendar is still in use today for all holidays (see the explanation in the Gregorian calendar ).

The Quartodecimanism (named after Latin quartodecimus = fourteenth) celebrated Easter as the Jews strictly on the 14th of Nisan, regardless of it which weekday is.

Table with data Easter, Ascension and Pentecost [ edit ]
The table below shows the data for the current time. The following data can be easily derived: ~ In a leap year, February 4
 * Carnival : usually calculated on the previous Sunday or Saturday to Shrove Tuesday.
 * Ash Wednesday : the day after Shrove Tuesday .
 * Palm Sunday, the Sunday before Easter.
 * Holy Week, the week before Easter. In this coming week: Maundy Thursday , Good Friday , Holy Saturday .
 * Easter Monday and Whit Monday, the Monday after the first Easter and Pentecost.

Future developments [ edit ]
Several churches are trying to bridge the differences in date of Easter and return to one calculation for the whole of Christendom [source?] . The greatest chance of acceptance is celebrating Easter according to the astronomical observation beginning of spring and full moon [source?] .

[Trivia Edit ]
A proverb says: That happens when Easter and Pentecost fall on one day, the meaning is: This will never happen, after all: Easter and Pentecost can not fall in a day.

Source [ edit ]
An earlier version of the text on this page comes from the website of the KNMI, with the mention: Thanks to Rob van Gent, Utrecht University .

Other frequent information from an article written by Hans van Maanen in Het Parool of March 30, 1991.