Calculate Easter with a Calculator
Easter is a Christian festival and holiday celebrating the resurrection of Jesus Christ on the third day after his crucifixion at Calvary as described in the New Testament of the Christian Bible. Easter is preceded by Lent, a forty-day period of fasting, penance, and prayer. The last week of Lent is called Holy Week, and it contains the days of the Easter Triduum, including Maundy Thursday, commemorating Maundy and the Last Supper, as well as Good Friday, commemorating the crucifixion and death of Jesus. Easter is followed by a fifty-day period called Eastertide or the Easter Season, ending with Pentecost Sunday. The festival is referred to in English by a variety of different names including Easter Day, Easter Sunday, Resurrection Day and Resurrection Sunday.
Easter is a moveable holiday, meaning it is not fixed in relation to the solar calendar. The First Council of Nicaea (325CE) established the date of Easter as the first Sunday after the following the northern hemisphere's vernal equinox. Ecclesiastically, the equinox is reckoned to be on March 21st (even though the equinox occurs, astronomically speaking, on March 20th in most years), and the "Full Moon" is usually not the astronomically correct date. The date of Easter therefore varies between March 22nd and April 25th. Eastern Christianity bases its calculations on the Julian calendar whose March 21st corresponds, during the 21st century, to April 3rd in the Gregorian calendar, in which the celebration of Easter therefore varies between April 4th and May 8th.
Easter is linked to the Jewish Passover by much of its symbolism, as well as by its position in the calendar. In many languages, the words for "Easter" and "Passover" are related etymologically or homonymous. Easter customs vary across the Christian world, but attending sunrise services, exclaiming the Easter greeting, clipping the church, decorating Easter eggs, a symbol of the empty tomb, are common motifs. Additional customs include egg hunting, the Easter Bunny, and Easter parades, which are observed by both Christians and some non-Christians.
In 725, Venerable Bede (I think he made up his own nickname) succinctly wrote, "The Sunday following the full Moon which falls on or after the equinox will give the lawful Easter." (See, succinct right?) However, this does not reflect the actual ecclesiastical rules precisely. One reason for this is that the full moon involved (called the Paschal full moon) is not an astronomical full moon, (of course back then they only had astrology, not astronomy, and forget about things like telescopes, they were still using leeches and blood lettings) but the 14th day of a calendar lunar month. Another difference is that the astronomical vernal equinox is a natural astronomical phenomenon, which can fall on March 19th, 20th, or 21st, while the ecclesiastical date is fixed by convention on March 21st (which is still wrong, but hey, priests aren't scientists, well, most of them aren't.)
In applying the ecclesiastical rules, Christian churches use March 21st as the starting point in determining the date of Easter, from which they find the next full moon. The Eastern Orthodox and Oriental Orthodox Churches continue to use the Julian calendar (because they thought that Gregorian guy was a jerk.) Their starting point in determining the date of Orthodox Easter is also March 21st, but according to the Julian reckoning, which currently corresponds to April 3rd in the Gregorian calendar. In addition, the lunar tables of the Julian calendar are four or five days behind those of the Gregorian calendar. (Can't we all just get along?) The 14th day of the lunar month according to the Gregorian system is only the 9th or 10th day according to the Julian. The result of this combination of solar and lunar discrepancies is divergence in the date of Easter in most years.
Easter is determined on the basis of lunisolar cycles. (Say that five times fast.) The lunar year consists of 30-day and 29-day lunar months, generally alternating, with an embolismic month (and then see your doctor) added periodically to bring the lunar cycle into line with the solar cycle. In each solar year the lunar month beginning with an ecclesiastical new moon falling in the 29-day period from March 8th through April 5th is designated as the paschal lunar month for that year. Easter is the third Sunday in the paschal (I keep wanting to draw triangles) lunar month, or, the Sunday after the paschal lunar month's 14th day. The 14th of the paschal lunar month is designated by convention as the Paschal full moon, although the 14th of the lunar month may differ from the date of the astronomical full moon by up to two days. Since the ecclesiastical new moon falls on a date from March 8th through April 5th, the paschal full moon must fall on a date from March 21st through April 18th.
Accordingly, Gregorian Easter can fall on 35 possible dates - March 22nd through April 25th. Now here is some interesting data, if you happen to like math, or astronomy, or if you're planning on going on Jeopardy! soon. It last fell on March 22nd in 1818, and will do so again in 2285. It fell on Marhc 23rd in 2008, but will not do so again until 2160. Easter last fell on the latest possible date, April 25th, in 1943 and will next fall on that date in 2038. However, it fell on April 24th, just one day before this latest possible date, in 2011 and will do so again in 2095. The cycle of Easter dates repeats after exactly 5,700,000 years, with April 19th being the most common date, happening 220,400 times or 3.9%, compared to the median for all dates of 189,525 times or 3.3%.
The Gregorian calculation of Easter was based on a method devised by the Calabrian doctor Aloysius Lilius (because he was bored and had nothing better to do at night) for adjusting the epacts of the moon, and has been adopted by almost all Western Christians and by Western countries who celebrate national holidays at Easter. For the British Empire and colonies (Do they still have those? I thought they all rebelled and were independent countries now.), a determination of the date of Easter Sunday using Golden Numbers (they're the shiny ones) and Sunday letters (who delivers mail on Sundays?) was defined by the Calendar (New Style) Act 1750 with its Annexe. This was designed to exactly match the Gregorian calculation.
The Greek island of Syros, whose population is divided almost equally between Catholics and Orthodox , is one of the few places where the two Churches share a common date for Easter, with the Catholics accepting the Orthodox date - a practice helping considerably in maintaining good relations between the two communities (because no one wants to start a war over which day to throw a party, though personally I'd suggest they all adopt both days, and have an even bigger shindig.)
In determining the date of the Gregorian and Julian Easter a lunisolar cycle is followed. In determining the date of the Jewish Passover a lunisolar calendar is also used, and because Easter always falls on a Sunday it usually falls up to a week after the first day of Passover. However, the differences in the rules between the Hebrew and Gregorian cycles results in Passover falling about a month after Easter in three years of the 19-year cycle. These occur in years 3, 11, and 14 of the Gregorian 19-year cycle (corresponding respectively to years 19, 8, and 11 of the Jewish 19-year cycle).
The reason for the difference is the different scheduling of embolismic months in the two cycles.
In addition, without changes to either calendar, the frequency of monthly divergence between the two festivals will increase over time as a result of the differences in the implicit solar years: the implicit mean solar year of the Hebrew calendar is 365.2468 days while that of the Gregorian calendar is 365.2425 days. In years 2200 - 2299, for example, the start of Passover will be about a month later than Gregorian Easter in four years out of nineteen. (And hopefully in the next 200 years someone will finally update them on how the solar system actually works.)
Since in the Modern Hebrew calendar Nisan 15 can never fall on Monday, Wednesday, or Friday, the seder of Nisan 15 never falls on the night of Maundy Thursday. The second seder, observed in some Jewish communities on the second night of Passover can, however, occur on Thursday night, and the resultant blue flus on the following Friday.
Because the Julian calendar's implicit solar year has drifted further over the centuries than those of the Gregorian or Hebrew calendars, Julian Easter is a lunation later than Gregorian Easter in five years out of nineteen, namely years 3, 8, 11, 14, and 19 of the Christian cycle. This means that it is a lunation later than Jewish Passover in two years out of nineteen, years 8 and 19 of the Christian cycle. (And you thought Algebra was hard to get through.) Furthermore, because the Julian calendar's lunar age is now about four to five days behind the mean lunations, Julian Easter always follows the start of Passover. This cumulative effect of the errors in the Julian calendar's solar year and lunar age has led to the often-repeated, but false, belief that the Julian cycle includes an explicit rule requiring Easter always to follow Jewish Passover. The supposed "after Passover" rule is called the Zonaras proviso, after Joannes Zonaras, the Byzantine canon lawyer who may have been the first to formulate it. (Because he was one of those oddballs who thinks math is fun.)
In Western Christianity, Easter is preceded by Lent, a period of fasting and penitence in preparation for Easter, which begins on Ash Wednesday and lasts forty days (not counting Sundays.)
The week before Easter, known as Holy Week, is very special in the Christian tradition. The Sunday before Easter is Palm Sunday, with the Wednesday before Pascha being known as Spy Wednesday. (I always rooted for the black one.) The last three days before Easter are Maundy Thursday, (no singing Barry Manilow, no matter how much you want to) Good Friday and Holy Saturday. Palm Sunday, Maundy Thursday and Good Friday respectively commemorate Jesus' entry in Jerusalem, the Last Supper and the Crucifixion. Maundy Thursday, Good Friday, and Holy Saturday are sometimes referred to as the Easter Triduum (Latin for "Three Days," in case you couldn't suss that out on your own). In some countries, Easter lasts two days, with the second called "Easter Monday". The week beginning with Easter Sunday is called Easter Week or the Octave of Easter, and each day is prefaced with "Easter", e.g. Easter Monday, Easter Tuesday, through Easter Saturday is therefore the Saturday after Easter Sunday. The day before Easter is properly called Holy Saturday. Many churches begin celebrating Easter late in the evening of Holy Saturday at a service called the Easter Vigil.
In Eastern Christianity, the spiritual preparation for Pascha begins with Great Lent, which starts on Clean Monday and lasts for 40 continuous days (including Sundays). The last week of Great Lent (following the fifth Sunday of Great Lent) is called Palm Week, and ends with Lazarus Saturday. (Because ho too rose from the dead.) The Vespers which begins Lazarus Saturday officially brings Great Lent to a close, although the fast continues through the following week. After Lazarus Saturday comes Palm Sunday, Holy Week, and finally Pascha itself, and the fast is broken immediately after the Paschal Divine Liturgy.
Yes, it's true(ish), you can use a simple calculator to figure out the date of Easter. Of course it's because Easter is based on astronomy and that's physics, and that's just math I don't really understand. But that just means that someone smarter than I am already figured out how to do it. Here's how:
There are three steps you'll have to go through to find the date of Easter with a calculator
Step 1: Get the Paschal Full Moon date from the table below.
Table 1 below shows the Paschal Full Moon dates from 326 through 2599CE. Use Table 2 for dates from 2600 through 4099.
1: Divide the year by 19.
For example, 2335 divided by 19 equals 122.8947368421053. Take .894 from the table and you have April 9, 2335CE.
Now you add the 3 numbers from the "Results" lines of Tables A, B, and C.
Continuing our earlier example of April 9, 2335 we get 0 from Table A. The 23 from 2335 give you 1 from Table B. The 35 from 2335 gives you 1 from Table C.
Add those three numbers, 0 + 1 + 1 = 2.
*1500 through 1582 use 4
Now you take your results from Step 2 and use those to find the day of the week on which the Paschal Full Moon falls. You then look that up in the final table below and from there you can calculate the date of Easter on whatever year you chose.
From our ealier example of 2335, we got the result of 2. Looking up in the final table we see that 2 corresponds with a Tuesday. We then add 5 days to our original date of April 9 to get April 14. And that, my friends is the date of Easter in the year 2335. Ta Da!