Hmmmm. If you ignore the pagan celebration of Oestre, then the first Easter began around 30 ad. Thus, there were no Easters before then. And, some factions of the Christian Church also have other definitions of Easter, or so I am told. I have always used the first Sunday after the first full moon after th Spring equinox. So, that adds some variables.
:) Simon --- Frank King <[EMAIL PROTECTED]> wrote: > Dear Mac, > > Many thanks for your message... > > > If you can find the time, this mailing list member > ... > > would much appreciate details about how you > derived the > > list of dates. > > I am glad you asked this question and equally glad > that Patrick Powers has supplied the algorithm! > > I had it in my head that this algorithm was first > published in Butcher's Ecclesiastical Handbook in > 1876 and I give this as the (incorrect) citation in > one of my sets of student exercises. > > When I Googled "Butcher's Ecclesiastical Handbook" > all I got was a couple of references to plagiarised > versions of my exercises. Tee hee! I wouldn't have > discovered my error had you not prompted me to look > for something else! > > I first saw the algorithm in Meeus and now see that > he > gives the correct citation "Butcher's Ecclesiastical > Calendar, 1876". > > There is a reasonably complete account in: > > http://en.wikipedia.org/wiki/Computus > > One of my favourite books is "Calendrical > Calculations" > by Edward M. Reingold and Nachum Dershowitz. It is > full of good jokes! > > This book almost attributes the algorithm to Clavius > and Lilius (key figures in the Gregorian reform of > the calendar). > > Once you have implemented the algorithm you can then > have fun determining the length of the cycle. A > naive approach is to start at an arbitrary year and > look for the next year that has Easter on the same > date. You then look to see whether the two > following > years match too. They won't! So you look for the > next matching year and keep going until you repeat > indefinitely. Your program will take a long time!! > > "Calendrical Calculations" says: > > The dates of Easter repeat only after 5,700,000 > years, the least common multiple of the 19-year > Metonic cycle, the 400 years it takes for the > Gregorian calendar to return to the same pattern > of days of the week, the 4000 years it takes for > the Gregorian leap-year corrections to add up to > 30 days, and the 9375 years it takes for the > correction to the Metonic cycle to amount to > 30 days. > > If you get to understand the ecclesiastical moon > and the ecclesiastical vernal equinox you will > wonder whether the algorithm works at all. In > fact it does a remarkably good job at predicting > "the first Sunday after the first full moon after > the vernal equinox" which is often given as the > formal definition of Easter. > > What I should like to know is what is meant by > Sunday! Sunday begins at different times in > different places. Could it mean Sunday as it > is timed at the longitude of Rome? > > Enough from me! > > Frank > > --------------------------------------------------- > https://lists.uni-koeln.de/mailman/listinfo/sundial > > --------------------------------------------------- https://lists.uni-koeln.de/mailman/listinfo/sundial
