Date of Easter

Western Christians celebrate Easter on the first Sunday after the full moon (the paschal moon) that occurs upon or next after the vernal equinox (taken as March 21). If the paschal moon, which is calculated from a system of golden numbers and epacts and does not necessarily coincide with the astronomical full moon, occurs on a Sunday, Easter day is the succeeding Sunday. Easter , therefore, can fall between March 22 and April 25. This rule was fixed after much controversy and uncertainty, which lasted in various parts of the church until the 8th century. In the Eastern Orthodox church , however, a slightly different calculation is followed, with the result that the Orthodox Easter , although sometimes coinciding with that of the West, can fall one, four, or five weeks later.

In the 20th century, the possibility of a fixed date for Easter has been discussed and supported among some Christians; adoption would depend on agreement being reached among the various churches. The second Sunday in April has been proposed.

Religious observances

The festival of Easter occurs on a particular Sunday, but its importance is emphasized in the worship of the church by the long preparation of Lent; by Holy Week, with its solemn services; and by the following 50 days until Pentecost (Whitsunday), a period known as Eastertide, or Paschaltide. Easter is central to the whole Christian year; not only does the entire ecclesiastical calendar of movable feasts depend upon its date but the whole liturgical year of worship is arranged around it. In the liturgical texts the emphasis is laid on its being the Christian Passover (the time of redemption).

By the time that the Christian liturgy had begun to take shape (2nd century), the Sunday Eucharist was preceded by a vigil service of Scripture readings and psalms. In this must be seen the origin of the Easter Vigil service, one of the striking celebrations of Easter in both East and West; from being a weekly observance the vigil has turned into an annual one at Easter only. As it is now constituted in the Roman Catholic missal, this vigil consists of the blessing of the new fire (a practice introduced during the early Middle Ages); the lighting of the paschal candle; a service of lessons, called the prophecies; followed by the blessing of the font and baptisms and then the mass of Easter . A similar form is used in Lutheran and some Anglican churches. This pattern is quite primitive and, in its principal elements, can be traced to the 3rd-4th century. In the course of time the vigil in the West (but never in the East) came to be celebrated on Saturday evening, then on Saturday afternoon, and finally, by the end of the Middle Ages, on Saturday morning. In 1951 (optionally) and 1955 (obligatorily) throughout the Roman Catholic church, the Easter vigil was restored to the starting time of about 10:00 PM, so that the first mass of Easter begins at midnight. Easter vigils in certain Protestant churches are similarly scheduled.

The connection of baptism with Easter is of early date. During the church's first centuries the whole of Lent was not only a time of penance but also the period during which the catechumens (persons to be baptized) were prepared for baptism, which was given only once a year, at Easter . For the six weeks preceding Easter the catechumens were instructed in the Christian faith, and the texts of the Lenten liturgy in the Roman Catholic missal still preserve clear indications of this practice. The catechumenate came to an end with the solemn baptisms of the Easter vigil. This is the explanation of the present practice of the long ceremony of blessing the font on Easter night and of the great emphasis on baptism and its meaning and the many allusions to it still present in the Easter services.

Among the Eastern Orthodox and Russian Orthodox churches, perhaps even greater emphasis is laid on the central position of Easter not only as an annual observance of the church year but as a centrepiece in the whole worship and spiritual life of the church. The vigil service is preceded by a procession outside the church representing a fruitless search for the body of Christ. Then comes the joyful announcement, "Christ is risen," followed by the Easter Eucharist. When the procession first leaves the church, there are no lights anywhere, but on its return hundreds of candles and coloured lamps are lighted to show the splendour of Christ's Resurrection.

In the Church of England the Book of Common Prayer provides special anthems to take the place of the Venite (Psalms 95) at matins. Lutheran hymnbooks, which contain orders of service, use special sentences at Easter . The Book of Common Order of the Church of Scotland includes prayers for Easter , and the Divine Worship of the Methodists has an order of worship for Easter morning, but the use of them is not compulsory.

In the Protestant churches, Easter Sunday observances are the culminating point of a series of services held during Holy Week, beginning with Palm Sunday. It is customary for the sacrament of Holy Communion to be administered during Holy Week, but the time of its observance varies. Many denominations have established the custom of celebrating Holy Communion on Maundy Thursday (the Thursday before Easter ); others administer the sacrament on Easter morning some time before the regularly established hour of worship. Many Protestant churches hold joint interdenominational Good Friday services, prepared under the auspices of the local ministerial association. These services in many communities centre on the traditional seven last "words" (or sayings) of Christ and are conducted from 12:00 noon to 3:00 PM with choirs and clergy of the participating denominations. This interdenominational pattern culminates in the Easter dawn service, which is of such interest in the United States that it commands wide television and radio coverage. The origin of the sunrise service is not known, but it would appear to be rooted in the Gospel narratives describing the Resurrection of Christ - e.g., John 20, "Now on the first day of the week, Mary Magdalene came to the tomb early, while it was still dark." Mingled with this biblical warrant is an association with the spring of the year and the idea of the new birth symbolized in nature's renewal of itself out of the death of winter.

Date of Easter during centuries

Easter was the most important feast of the Christian Church, and its place in the calendar determined the position of the rest of the church's movable feasts (see church year ). Because its timing depended on both the Moon's phases and the vernal equinox, ecclesiastical authorities had to seek some way of reconciling lunar and solar calendars. Some simple form of computation, usable by non-astronomers in remote places, was desirable. There was no easy or obvious solution, and to make things more difficult there was no unanimous agreement on the way in which Easter should be calculated, even on a lunar calendar.

Easter , being the festival of the Resurrection, had to depend on the dating of the Crucifixion, which occurred three days earlier and just before the Jewish Passover. The Passover was celebrated on the 14th day of Nisan, the first month in the Jewish religious year - that is, the lunar month the 14th day of which falls on or next after the vernal equinox. The Christian churches in the eastern Mediterranean area celebrated Easter on the 14th of Nisan on whatever day of the week it might fall, but the rest of Christendom adopted a more elaborate reckoning to ensure that it was celebrated on a Sunday in the Passover week.

To determine precisely how the Resurrection and Easter Day should be dated, reference was made to the Gospels; but, even as early as the 2nd century AD, difficulties had arisen, because the synoptic Gospels (Matthew, Mark, and Luke) appeared to give a different date from the Gospel According to John for the Crucifixion. This difference led to controversy that was later exacerbated by another difficulty caused by the Jewish reckoning of a day from sunset to sunset. The question arose of how the evening of the 14th day should be calculated, and some - the Quintodecimans - claimed that it meant one particular evening, but others - the Quartodecimans - claimed that it meant the evening before, since sunset heralded a new day. Both sides had their protagonists, the Eastern churches supporting the Quartodecimans, the Western churches the Quintodecimans. The question was finally decided by the Western church in favour of the Quintodecimans, though there is debate whether this was at the Council of Nicaea in 325 or later. The Eastern churches decided to retain the Quartodeciman position, and the church in Britain, which had few links with European churches at this time, retained the Quartodeciman position until Roman missionaries arrived in the 6th century, when a change was made. The dating of Easter in the Gregorian calendar was based on the decision of the Western church, which decreed that Easter should be celebrated on the Sunday immediately following the (Paschal) Full Moon that fell on or after the vernal equinox, which they took as March 21. The church also ordered that if this Full Moon fell on a Sunday, the festival should be held seven days later.

With these provisions in mind, the problem could be broken down into two parts: first, devising a simple but effective way of calculating the days of the week for any date in the year and, second, determining the date of the Full Moons in any year. The first part was solved by the use of a letter code derived from a similar Roman system adopted for determining market days. For ecclesiastical use, the code gave what was known as the Sunday, or dominical, letter.

The seven letters A through G are each assigned to a day, consecutively from January 1 so that January 1 appears as A, January 2 as B, to January 7 which appears as G, the cycle then continuing with January 8 as A, January 9 as B, and so on. Then in any year the first Sunday is bound to be assigned to one of the letters A–G in the first cycle, and all Sundays in the year possess that dominical letter. For example, if the first Sunday falls on January 3, C will be the dominical letter for the whole year. No dominical letter is placed against the intercalary day, February 29, but, since it is still counted as a weekday and given a name, the series of letters moves back one day every leap year after intercalation. Thus, a leap year beginning with the dominical letter C will change to a year with the dominical letter B on March 1; and in lists of dominical letters, all leap years are given a double letter notation, in the example just quoted, CB. It is not difficult to see what dominical letter or letters apply to any particular year, and it is also a comparatively simple matter to draw up a table of dominical letters for use in determining Easter Sunday. The possible dates on which Easter Sunday can fall are written down - they run from March 22 through April 25 - and against them the dominical letters for a cycle of seven years. Once the dominical letter for a year is known, the possible Sundays for celebrating Easter can be read directly from the table. This system does not, of course, completely determine Easter ; to do so, additional information is required.

This must provide dates for Full Moons throughout the year, and for this a lunar cycle like the Metonic cycle was originally used. Tables were prepared, again using the range of dates on which Easter Sunday could appear, and against each date a number from one through 19 was placed. This number indicated which of the 19 years of the lunar cycle would give a Full Moon on that day. From medieval times these were known as golden numbers, possibly from a name used by the Greeks for the numbers on the Metonic cycle or because gold is the colour used for them in manuscript calendars.

The system of golden numbers was introduced in 530, but the numbers were arranged as they should have been if adopted at the Council of Nicaea two centuries earlier; and the cycle was taken to begin in a year when the New Moon fell on January 1. Working backward, chronologers found that this date had occurred in the year preceding AD 1, and therefore the golden number for any year is found by adding one to the year and dividing that sum by 19. The golden number is the remainder or, if there is no remainder, 19.

To compute the date of Easter , the medieval chronologer computed the golden number for the year and then consulted his table to see by which date this number lay. Having found this date, that of the first Full Moon after March 20, he consulted his table of dominical letters and saw the next date against which the dominical letter for that year appeared; this was the Sunday to be designated Easter . The method, modified for dropping centennial leap years as practiced in the Gregorian calendar, is still given in the English prayer book, although it was officially discarded when the Gregorian calendar was introduced.

The system of golden numbers was eventually rejected because the astronomical Full Moon could differ by as much as two days from the date they indicated. It was Lilius who had proposed a more accurate system based on one that had already been in use unofficially while the Julian calendar was still in force. Called the epact - the word is derived from the Greek epagein, meaning "to intercalate" - this was again a system of numbers concerned with the Moon's phases, but now indicating the age of the Moon on the first day of the year, from which the age of the Moon on any day of the year may be found, at least approximately, by counting, using alternately months of 29 and 30 days.

The epact as previously used was not, however, completely accurate because, like the golden number, it had been based on the Metonic cycle. This 19-year cycle was in error, the discrepancy amounting to eight days every 2,500 years. A one-day change on certain centennial years was then instituted by making the computed age of the Moon one day later seven times, at 300-year intervals, and an eighth time after a subsequent 400 years. This operation was known as the lunar correction, but it was not the only correction required; there was another.

Because the Gregorian calendar used a more accurate value for the tropical year than the Julian calendar and achieved this by omitting most centennial leap years, Clavius decided that, when the cycle of epacts reached an ordinary centennial year, the number of the epact should be reduced by one; this reduction became known as the solar correction.

One advantage of the epact number was that it showed the age of the Moon on January 1 and so permitted a simple calculation of the dates of New Moon and Full Moon for the ensuing year. Another was that it lent itself to the construction of cycles of 30 epact numbers, each diminishing by one from the previous cycle, so that, when it became necessary at certain centennial years to shift from one cycle to another, there would still be a cycle ready that retained a correct relationship between dates and New Moons.

For determining Easter , a table was prepared of the golden numbers, one through 19, and below them the cycles of epacts for about 7,000 years; after this time, all the epact cycles are repeated. A second table was then drawn up, giving the dates of Easter Full Moons for different epact numbers. Once the epact for the year was known, the date of the Easter Full Moon could be immediately obtained, while consultation of a table of dominical letters showed which was the next Sunday. Thus, the Gregorian system of epacts, while more accurate than the old golden numbers, still forced the chronologer to consult complex astronomical tables.