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The commonly stated rule that Easter is the first Sunday after the first full moon after the vernal
equinox is not quite correct. Easter is actually the first Sunday strictly after the "Paschal full moon"
(i.e., if the Paschal full moon falls on a Sunday, Easter is the following Sunday). The date of the
Paschal full moon is determined from tables, and it may differ from the date of the actual full moon
by up to two days (Marcos).
The possible dates for the Paschal full moon are March 21 through April 18. This gives the date of Easter as
March 22 through April 25. The days on which Easter occurs repeat with a period of 1,900,000 years, and consecutive
Easters are always separated by 350, 357, 378, or 385 days. The day on which Easter occurs can by found using
EasterSunday[y] in the Mathematica
add-on package Miscellaneous`Calendar` (which can be loaded with the command <<Miscellaneous`). The following table gives the dates for Easter between 1980 and 2009.
| 1980 |
April 6 |
1990 |
April 15 |
2000 |
April 23 |
| 1981 |
April 19 |
1991 |
March 31 |
2001 |
April 15 |
| 1982 |
April 11 |
1992 |
April 19 |
2002 |
March 31 |
| 1983 |
April 3 |
1993 |
April 11 |
2003 |
April 20 |
| 1984 |
April 22 |
1994 |
April 3 |
2004 |
April 11 |
| 1985 |
April 7 |
1995 |
April 16 |
2005 |
March 27 |
| 1986 |
March 30 |
1996 |
April 7 |
2006 |
April 16 |
| 1987 |
April 19 |
1997 |
March 30 |
2007 |
April 8 |
| 1988 |
April 3 |
1998 |
April 12 |
2008 |
March 23 |
| 1989 |
March 26 |
1999 |
April 4 |
2009 |
April 12 |
According to a British correspondent, the Book of Common Prayer (enshrined in English Law around 1526) defines Easter day
as the first Sunday after the full moon, which happens upon, or next after the twenty first day of March; and if
the full moon happens upon a Sunday, Easter Day is the Sunday after. This would appear to contract the use of the
Paschal full moon.
 Epact, Full Moon, Golden Number, Paschal Full Moon
de Morgan, A. A Budget of Paradoxes, 2nd ed., 2 vols. Freeport, NY: Books for Libraries Press, 1969.
Duffett-Smith, P. "The Date of Easter." §2 in Practical Astronomy with Your Calculator, 3rd ed.
Cambridge, England: Cambridge University Press, pp. 2-3, 1992.
Marcos, M. "Calculation of the Ecclesiastical Calendar." http://www.smart.net/~mmontes/ec-cal.html.
Seidelmann, P. K. Explanatory Supplement to the Astronomical Almanac.
Mill Valley, Calif.: University Science Books, 1992.
Stewart, I. "Mathematical Recreations: Calculating the Date of Easter." Sci. Amer. 284, 88-89, Mar. 2001.
Tøndering, C. "Frequently Asked Questions about Calendars." http://www.tondering.dk/claus/calendar.html.
© 1996-2007 Eric W. Weisstein
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