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Sunday, 01 April, 2007

Today Is Not Easter
(with comments)

Up until about 9:30 am, I thought today was Easter. But Pamn set me straight. Easter is next Sunday.

Speaking of holidays: April Fools Day: The Real Christian Holiday.

What does April Fools Day have to do with Christianity? Everything. This pseudo-holiday, recognized but not celebrated, is about gullibility. As gullibility is a vital friend to religion, it seems that Christians should recognize this as an important holiday. April Fools is about playing pranks, about telling lies, and about trying to convince someone that something is true when you know it isn't. The parallels with Christianity are striking.

Here's some trivia. The last time Easter was on April Fool's day was in 1956. The next time it happens will be in 2018. I figured this out by using this weird Excel formula (cell A1 contains a year):

=DOLLAR(("4/"&A1)/7+MOD(19*MOD(A1,19)-7,30)*14%,)*7-6

I calculated the date of Easter for 300 years, beginning in 1900. Then created a pivot table and pivot chart. I learned that, during this 300-year period, the most common day for Easter is March 31. The least common day is March 24.


Permalink | Posted in Excel |
  1. By reddog. Comment posted 01-Apr-2007 @10:39am:
    I celebrate Yeaster. I mix Barley malt with hops and water.

    On the third day, beer rises.

    Yum!
  2. By mmmark. Comment posted 01-Apr-2007 @11:38am:
    Nicely charted. But the data is inaccurate. Instead of multiplying by 14%, you should use the more precise calendar factor of .14245.
    It affects six of your dates.
  3. By causal_sailor. Comment posted 01-Apr-2007 @12:09pm:
    Thanks for running this down! In a moment driving one day, I'd wondered about the date distribute and had figured the average date must be 18 days after the equinox. Here's why I thought this:

    Easter is the first Sunday after the first full moon after the spring equinox. The mean time to the first full moon would occur 14 3/4 days after the 21st. Then the first sunday after that would be, on the average, 3 1/2 days after the full moon. I'm not sure how the rounding on this is handled since I don't know what the fine print says (and is it the first full moon after the actual equinox? or the first one after the 21st? I think it is the latter.) In any case, My thinking in the car that day made me think the middle of the distribution would fall on March 21 + 18 1/4 days. With a 300 year sample, you've revealed that I was wrong. I suspect the error lies in the lunar cycle part of my reasoning.
  4. By DaveR. Comment posted 01-Apr-2007 @12:19pm:
    Did you run this on a palm-top?
  5. By J-Walk. Comment posted 01-Apr-2007 @12:58pm:
    mmmark, changing .14 to .14245 does indeed affect six dates. But those six dates are wrong using .14245. At least according to this site:

    http://www.holidays.net/easter/eadates.htm

    Oh wait! This is April Fool's day. You got me!
  6. By Andie. Comment posted 01-Apr-2007 @02:22pm:
    My sister was born on Easter in 1947. We were told that her birthday would fall on Easter every 11 years. That only worked in 1958, 1969 and 1980. I actually don't care so I haven't paid any attention to it for many years.
  7. By John Wilson. Comment posted 01-Apr-2007 @03:09pm:
    Speaking of April Fools....
    I happened upon this (Toilet Internet Service Protocol):

    http://www.google.com/tisp/index.html

    When those Google folks make up a joke site they really do a great job.

    Check out the "How TiSP works" link.
    Enjoy
  8. By YetAnotherDave. Comment posted 01-Apr-2007 @04:04pm:
    The usual statement, that Easter Day is the first Sunday after the full moon that occurs next after the vernal equinox, is not a precise statement of the actual ecclesiastical rules. The full moon involved is not the astronomical Full Moon but an ecclesiastical moon (determined from tables) that keeps, more or less, in step with the astronomical Moon.

    The ecclesiastical rules are:

    · Easter falls on the first Sunday following the first ecclesiastical full moon that occurs on or after the day of the vernal equinox;
    · this particular ecclesiastical full moon is the 14th day of a tabular lunation (new moon); and
    · the vernal equinox is fixed as March 21.

    As a result, Easter can never occur before March 22 or later than April 25.
  9. By YetAnotherDave. Comment posted 01-Apr-2007 @04:13pm:
    ' Incidentally, here is an algorithm for VBA that is derived from one published by J. M. Oudin (1940)for calculating the date of Easter:

    y = Int(Val([TextStringDate]))
    c = Int(y / 100)
    n = y - 19 * Int((y / 19))
    k = Int((c - 17) / 25)
    i = c - Int(c / 4) - Int((c - k) / 3) + 19 * n + 15
    i = i - 30 * Int((i / 30))
    i = i - Int((i / 28)) * (1 - Int((i / 28)) * Int((29 / (i + 1))) * Int(((21 - n) / 11)))
    j = y + Int(y / 4) + i + 2 - c + Int(c / 4)
    j = j - 7 * Int((j / 7))
    l = i - j
    m = 3 + Int((l + 40) / 44)
    d = l + 28 - 31 * Int((m / 4))

    Easter = Months(m) + Str$(d) + "," + Str$(y)
  10. By Bisbonian. Comment posted 01-Apr-2007 @04:30pm:
    "The name "Easter" originated with the names of an ancient Goddess and God. The Venerable Bede, (672-735 CE.) a Christian scholar, first asserted in his book De Ratione Temporum that Easter was named after Eostre (a.k.a. Eastre). She was the Great Mother Goddess of the Saxon people in Northern Europe. Similarly, the "Teutonic dawn goddess of fertility [was] known variously as Ostare, Ostara, Ostern, Eostra, Eostre, Eostur, Eastra, Eastur, Austron and Ausos." 1 Her name was derived from the ancient word for spring: "eastre." Similar Goddesses were known by other names in ancient cultures around the Mediterranean, and were celebrated in the springtime. Some were:

    Aphrodite from ancient Cyprus
    Ashtoreth from ancient Israel
    Astarté from ancient Greece
    Demeter from Mycenae
    Hathor from ancient Egypt
    Ishtar from Assyria
    Kali, from India
    Ostara a Norse Goddess of fertility."

    http://www.religioustolerance.org/easter1.htm
  11. By MAPLE LEAF. Comment posted 01-Apr-2007 @04:41pm:
    It's not easter? Well, I am eating my way through this six-pack of lavender Peeps anyhow.
  12. By biff. Comment posted 01-Apr-2007 @07:54pm:
    Reading how the date for Easter is established makes my head hurt.

    Compressing all that babble into that short formula is impressive.
  13. By EEK-A-CELL. Comment posted 01-Apr-2007 @09:41pm:
    I prefer this version it calculates the date of Gregorian Easter for any date entered.
    =DOLLAR(("4/"&DAY;(MINUTE(YEAR(A1)/38)/2+55)&"/"&YEAR;(A1))/7,)*7-6
  14. By Terry. Comment posted 02-Apr-2007 @01:46am:
    As it just so happens... I was born on Good Friday of 1972. March 31st, the most popular Easter Day according to the chart.
  15. By REHOP. Comment posted 02-Apr-2007 @04:50am:
    There are a number of differences between YetAnotherDave's formula and yours after 2199. Any idea why? I don't want to get the wrong date, just in case I live to be 257 (Excel formula =2204-1947).
  16. By mrcaribou. Comment posted 02-Apr-2007 @05:30am:
    All I can say for sure is that you are wrong in your calculations somewhere. Easter in 1956 was on April 8th. Just like it is this year. I'm living proof.
    Mr Caribou
  17. By Snag. Comment posted 02-Apr-2007 @06:20am:
    Had a play with the "J-Walk" formula. The host cell, of course, has to be date formatted to make sense. Interesting that it works (returns a result) from 1900 to 9999, but not outside those dates. If society's background assumptions were not so contrived I might be more inclined to explore the means by which it arrives at its result.

    EEK-A-CELL .. yours returns a value error. I gave up at that point.
  18. By Snag. Comment posted 02-Apr-2007 @06:29am:
    mrcaribou seems to be correct, even by the link in comment #5. Seems to me that the matter is so convoluted, a universal formula might be quite a stretch.
  19. By J-Walk. Comment posted 02-Apr-2007 @06:52am:
    This is pretty interesting. Lots of sources on the Web say that Easter in 1956 was April 1, yet two people here claim it was April 8.

    And here's a source that claims it was April 2.
  20. By Dave (TDC). Comment posted 02-Apr-2007 @08:46am:
    It was my birthday last Thursday (29th) & I was born on an Easter Sunday, using the formulae above you should be able to calculate my age given it is an even number and I am of the youngest age possible with those criteria. (but I'd rather you didn't bother).

    Extra clue - I'm younger than Louie Louie
  21. By south. Comment posted 02-Apr-2007 @09:03am:
    interesting
    http://www.holidays.net so far gave
    April 25, 1965
    April 22, 1965
    April 1, 1965
    April 8, 1965
    ...
  22. By south. Comment posted 02-Apr-2007 @09:05am:
    typo - should be 1956, not '65
  23. By Imagineer. Comment posted 02-Apr-2007 @09:25am:
    All the same, south, I'd rather have Earth Day on my birthday than Easter.
  24. By GlennInBR. Comment posted 02-Apr-2007 @10:57pm:
    I get April 1 in 1956 from both the Oudin algorithm and from the Butcher algorithm:

    dA = iYear - 19 * (iYear \ 19)
    dCentury = iYear \ 100
    dYrInCentury = iYear - (dCentury * 100)
    dD = dCentury \ 4
    dE = dCentury - (dD * 4)
    dF = (dCentury + 8) \ 25
    dG = (dCentury - dF + 1) \ 3
    dH = (19 * dA + dCentury - dD - dG + 15) Mod 30
    dI = dYrInCentury \ 4
    dK = dYrInCentury - (dI * 4)
    dL = (32 + 2 * dE + 2 * dI - dH - dK) Mod 7
    dM = (dA + 11 * dH + 22 * dL) \ 451
    dQ = (dH + dL - 7 * dM + 114)
    oMonth = dQ \ 31
    oDayOfMonth = (dQ Mod 31) + 1

    (YetAnotherDave's first line of code may seem mysterious; it's supposed to extract just the year from a date.)
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