Easter Sunday will be April 17. An even greater frequency of airplanes passing overhead from Heathrow reminds us that Britain’s Easter vacations have started. Many other fixtures in the calendar, such as Lent and Palm Sunday and Good Friday, depend on Easter Sunday, and Easter Sunday is anything but dependable!
The date of Easter is intended to be the Sunday after the full Moon that is on or after the day of the vernal equinox. But the equinox is equated with March 21 (whereas astronomically it may occur on March 19, 20, or 21). The date assumed for the full Moon, too, may not coincide exactly with the astronomical one. So Easter is in practice determined from formulae (Golden Numbers and Epacts).
The results is that Easter Sunday can be anywhere between March 22 and April 25.
Here is a graph for two decades. The red dots are at the true days of full Moon, and the blue bars are at Sundays.
The distribution of the Easter Sundays over the calendar looks like an almost random scatter. The irregularity arises because there are three factors: March 21, which is fixed, and full Moon and Sunday, both of which vary from year to year. Sunday, like any week day, becomes each year one day earlier in the month or sometimes two; full Moon dates fall each year 10 or 11 or 12 days earlier in the month.
If Easter was always just the first Sunday after March 21, or the first full Moon after March 21, our calendar would be considerably more regular – freed from its wobble, let’s say. One is tempted to think the Easter rule a nuisance like the clock-changing “daylight-shifting” rule!
Like Easter wandering with the moon
we seek through April into June…
__________
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I’m glad you noted that Easter Sunday is determined mathematically, according to the phases of a hypothetical moon, and not according to the phases of the actual, physical moon, as many people seem to think. This is necessary to avoid the problem of an Easter date dependent on longitude. This year provides a prime example. The actual full moon occurs on 16 April at 18:55 UTC, resulting in Easter Sunday on 17 April for most of the world. However for locations at far eastern longitudes such as Sydney, where I live, the actual full moon occurs on 17 April at 04:55, theoretically resulting in Easter Sunday on 24 April.
Good point. But I would think that the basic reason for continuing to use formulae worked out centuries ago is that otherwise, for the determination of the instant of full moon, there would have to be reliance on programmers using the eoab0rate modern equations for the moon’s motion.
Over the years I’ve often heard people say, “Easter is early this year” or, just as often, “Easter is late this year”.
But I’ve never heard anyone say,
“Easter is right on time this year!”.
Does not appear so random to me. Throw out 2022 and I am seeing a top left to lower right progression on a 3 year cycle with each new cycle sorta starting starting every 5 years (2020, 2025, 2030). If I can find my old Jean Meeus calculations book I used to program my TRS-80 way back in the day I’d be interested in seeing what happens if we add 2000 – 2020 and 2040-2060 to the chart. Of course, if I knew someone that was already set up to calculate the dates and graph them in the same manner…….(hint, hint)
Charles, I’ll calculate and send you a list of Easter dates 2000-2050.
I’d send you the graph, but it would be a large file of type .eps which you probably couldn’t open.
This website has the years of the 2000’s & 2010’s listed by date. It is interesting to notice that Easter dates that repeat do so with either an 11 or 5/6 day (leap year effect?) period. Haven’t had a chance to work through the math but I’m sure 7 day weeks, ~29 lunar periods, & leap years would contribute to any “pattern”. i.e.:
March 22nd
March 23rd 2008
March 24th
March 25th 2035, 2046
March 26th 2062, 2073, 2084
March 27th 2005, 2016
March 28th 2027, 2032, 2100
March 29th 2043, 2054, 2065
March 30th 2059, 2070, 2081, 2092
March 31st 2002, 2013, 2024, 2086, 2097
April 1st 2018, 2029, 2040
April 2nd 2051, 2056
April 3rd 2067, 2078, 2089
April 4th 2010, 2021, 2083, 2094
April 5th 2015, 2026, 2037, 2048
April 6th 2042, 2053, 2064
April 7th 2075, 2080
April 8th 2007, 2012, 2091
April 9th 2023, 2034, 2045
April 10th 2039, 2050, 2061, 2072
April 11th 2004, 2066, 2077, 2088
April 12th 2009, 2020, 2093, 2099
April 13th 2031, 2036
April 14th 2047, 2058, 2069
April 15th 2001, 2063, 2074, 2085, 2096
April 16th 2006, 2017, 2028, 2090
April 17th 2022, 2033, 2044
April 18th 2049, 2055, 2060
April 19th 2071, 2076, 2082
April 20th 2003, 2014, 2025, 2087, 2098
April 21st 2019, 2030, 2041, 2052
April 22nd 2057, 2068
April 23rd 2079
April 24th 2011, 2095
April 25th 2038
Top right to lower left, duh. Thanks
Ah but there’s also this lovely star picture behind the mystery, in that Sun returns to the northern celestial hemisphere and then awaits the proper witness, the Moon, to “acknowledge its return,” as it were, by coming Full below the celestial equator from now until Autumn, when it reverses again. I particularly like the moment of moonrise and sunset once the Vernal Moon has come Full, when Sun is above the equator and below the horizon, while Moon is above the horizon and below the equator. That’s when we are “east of the sun and west of the moon” and smack in the midst of a cosmic mystery!
I don’t have a reference right at hand, but the Roman Catholic Vatican II Ecumenical Council noted the Church was not ruling out a fixed date for Easter. Of course, then you’d still have Passover and Ramadan as movable feasts.
From the Appendix to Sacrosanctum Concilium (Constitution on the Sacred Liturgy):
“The Sacred Council would not object if the feast of Easter were assigned to a particular Sunday of the Gregorian Calendar, provided that those whom it may concern, especially the brethren who are not in communion with the Apostolic See, give their assent.”