Easter

=== Computations ===
In 725, [[Bede]] succinctly wrote, "The Sunday following the full Moon which falls on or after the [[equinox]] will give the lawful Easter."<ref>{{cite book|last=Wallis|first=Faith|title=Bede: The Reckoning of Time|date=1999|publisher=Liverpool University Press|isbn=0853236933|page=[https://books.google.com/books?id=yFsw-Vaup6sC&pg=PA148 148]|title-link=The Reckoning of Time}}</ref> However, this does not precisely reflect the ecclesiastical rules. The full moon referred to (called the [[Paschal full moon]]) is not an astronomical full moon, but the [[ecclesiastical full moon|14th day]] of a [[lunar month]]. Another difference is that the [[Equinox|astronomical equinox]] is a natural astronomical phenomenon, which can fall on 19, 20 or 21 March,<ref>[http://earthsky.org/astronomy-essentials/full-moon-vernal-equinox-date-of-easter Why is Easter so early this year?] {{Webarchive|url=https://web.archive.org/web/20210419030303/https://earthsky.org/astronomy-essentials/full-moon-vernal-equinox-date-of-easter |date=19 April 2021 }}, EarthSky, Bruce McClure in Astronomy Essentials, 30 March 2018.</ref> while the ecclesiastical date is fixed by convention on 21 March.<ref>Paragraph 7 of [[Inter gravissimas]] [http://isotc.iso.org/livelink/livelink/fetch/2000/2122/138351/138352/1311683/4020763/2015225/8601RevN005_Inter_Gravissimas.pdf?nodeid=2179035&vernum=0refers ISO.org] {{Webarchive|url=https://web.archive.org/web/20220714160228/https://login.iso.org/idp/SSO.saml2?SAMLRequest=fVLLbsIwEPyVyPe8HMTDIpFSOBSJloikPfSCTLKAVWOnXoe2f98k0EIvXFaWdnZmdrxT5EdZs7SxB7WGjwbQOl9HqZD1jZg0RjHNUSBT%2FAjIbMny9GnJqBew2mirSy2JkyKCsUKrmVbYHMHkYE6ihJf1MiYHa2tkvi9Q29Jrq6fN3pfiBFKo9%2BsjP4jtVkuwBw9R%2B50M9bNVXhBn3voSincKVz6p90L98Ymq9vN85XW%2BKXEW85hsgircReMxn0xgwMOKB5wOYAhRWUbDakijFobYwEKh5crGhAaUusHIDQdFOGQBZXT0RpzssuaDUJVQ%2B%2FuZbM8gZI9Fkbln969gsHfeAkgy7RyyXtjcZH2flv8GTJIOdlma8bqWouxzcSvYdT9Sbdrmps966t9InXVr9txyL%2BaZbue%2BnVRK%2FTkzwC3EJCR%2Bch75fxDJDw%3D%3D&RelayState=https%3A%2F%2Fisotc.iso.org%2Flivelink%2Flivelink%2Ffetch%2F2000%2F2122%2F138351%2F138352%2F1311683%2F4020763%2F2015225%2F8601RevN005_Inter_Gravissimas.pdf%3Fnodeid%3D2179035%26vernum%3D0refers&SigAlg=http%3A%2F%2Fwww.w3.org%2F2000%2F09%2Fxmldsig%23rsa-sha1&Signature=frB%2BJ%2FurXZDghPJm9huiZCq14gY2WIeGWOFOoWlNxfvWrDpaTEOudKYAui7nbgBTBkZArsQGvs5AgK4U1au3iifHt83yClQ5j4VHpDHqXJjilPM%2FzL6hgwl1uwU1hoykZ1V8URkAUazJRUvJlSaboeRRYQtIm1bDLAZLF%2BS3t58%3D |date=14 July 2022 }} to "the vernal equinox, which was fixed by the fathers of the [first] [[First Council of Nicaea|Nicene Council]] at XII calends April [21 March]". This definition can be traced at least back to chapters 6 & 59 of [[Bede]]'s ''[[De temporum ratione]]'' (725).</ref>

In addition, the lunar tables of the Julian calendar are currently five days behind those of the Gregorian calendar. Therefore, the Julian computation of the Paschal full moon is a full five days later than the astronomical full moon. The result of this combination of solar and lunar discrepancies is divergence in the date of Easter in most years (see table).<ref name="dateACC">{{cite web |title=Date of Easter |url=https://www.anglican.ca/ask/faq/easter/ |website=The Anglican Church of Canada |access-date=5 April 2021 |archive-date=26 December 2021 |archive-url=https://web.archive.org/web/20211226225037/https://www.anglican.ca/ask/faq/easter/ |url-status=live }}</ref>

Easter is determined on the basis of [[lunisolar calendar|lunisolar]] cycles. The lunar year consists of 30-day and 29-day lunar months, generally alternating, with an [[embolismic month]] added periodically to bring the lunar cycle into line with the solar cycle. In each solar year (1 January to 31 December inclusive), the lunar month beginning with an [[ecclesiastical new moon]] falling in the 29-day period from 8 March to 5 April inclusive is designated as the paschal lunar month for that year.<ref name="smart.net">Montes, Marcos J. [http://www.smart.net/~mmontes/ec-cal.html "Calculation of the Ecclesiastical Calendar"] {{webarchive |url=https://web.archive.org/web/20081103111329/http://www.smart.net/~mmontes/ec-cal.html |date=3 November 2008 }}. Retrieved 12 January 2008.</ref>

Easter is the third Sunday in the paschal lunar month, or, in other words, 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.<ref name="smart.net"/> Since the ecclesiastical new moon falls on a date from 8 March to 5 April inclusive, the paschal full moon (the 14th of that lunar month) must fall on a date from 22 March to 18 April inclusive.<ref name="dateACC"/>

The Gregorian calculation of Easter was based on a method devised by the [[Calabria]]n doctor [[Aloysius Lilius]] (or Lilio) for adjusting the [[epact]]s of the Moon,<ref>G Moyer (1983), [http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?journal=grc..&year=1983&volume=book&page_ind=181 "Aloisius Lilius and the 'Compendium novae rationis restituendi kalendarium'"] {{Webarchive|url=https://web.archive.org/web/20211012082725/http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?journal=grc..&year=1983&volume=book&page_ind=181 |date=12 October 2021 }}, pp. 171–188 in G.V. Coyne (ed.).</ref> and has been adopted by almost all Western Christians and by Western countries which celebrate national holidays at Easter. For the British Empire and colonies, a determination of the date of Easter Sunday using [[Golden number (time)|Golden Numbers]] and [[Dominical letter|Sunday letters]] was defined by the [[Calendar (New Style) Act 1750]] with its Annexe. This was designed to match exactly the Gregorian calculation.<ref name="legislation.gov.uk-calendar">{{cite web |title=Calendar (New Style) Act 1750 |url=https://www.legislation.gov.uk/apgb/Geo2/24/23 |website=legislation.gov.uk|access-date=23 April 2023|archive-date=April 23, 2023 |archive-url=https://web.archive.org/web/20230423123410/https://www.legislation.gov.uk/apgb/Geo2/24/23 |url-status=live }}</ref>