Late Easter

In the Western Church calendar, Easter is a movable feast where Easter Sunday is defined to be the first Sunday after the Full Moon that occurs on or after the day of the ecclesiastical spring equinox, defined as the 21st March. Thus, Easter can occur as early as 22nd March or as late as 25th April. In the northern hemisphere, the equinoxes occur in March (vernal) and September (autumnal), and are the two occasions each year when the day and the night are of nearly equal length.

An equinox (which is Latin for "equal night") is defined as the moment when the sun reaches one of two intersections between the ecliptic and the celestial equator. The astronomical Spring Equinox varies slowly between the 19th and 21st March, and for the remainder of this century mostly falls on the 20th March (it is not until 2044 that it first falls on another date, namely 19th March). This year, the vernal equinox occurred on 20th March and the first Full Moon following this will be that of Monday, 18th April. So this year Easter Sunday, that is the first Sunday after this Full Moon, falls on 24th April.

This is nearly the latest possible date for Easter Sunday. The last time Easter Sunday was at least this late was 1943 (25th April) and it will not be this late again until 2038 (also 25th April). By contrast, just three years ago, Easter occurred nearly as early as it could do, namely 23rd March 2008.

FOR FURTHER INFORMATION PLEASE CONTACT: John McFarland at the Armagh Observatory, College Hill, Armagh, BT61 9DG. Tel.: 028-3752-2928; FAX: 028-3752-7174; jmfat signarm.ac.uk.

Last Revised: 2011 April 8th