Under what circumstances exactly will a 50 year anniversary fall on the same day of the week as the original date? Today (6 June 2004) is a Sunday, and so was 6 June 1954. Ignore all the old calendar stuff, let's say I'm only interested in this question for dates after 1800. There seem to be lots of web pages about "repeating calendar years" but that's not at all the same question since dates can agree on day of the week even when they differ on leap year status... I was asked this at a wedding anniversary party and stammered something about 100 year leap year cycles with 400 year exceptions but couldn't work out the general answer, at least with dance music playing Thane Plambeck 650 321 4884 office 650 323 4928 fax http://www.plambeck.org
Under what circumstances exactly will a 50 year anniversary fall on the same day of the week as the original date?
If one ignores leap-year days, 50 years equals 2607 weeks and one day. So the anniversary will occur on the same weekday if there are 6,13,20,27,... leap days. But leap days occur almost every fourth year: there are always 11-13 of them in a 50-year span. We want 13. That happens when the date is not a leap day, occurs less than two years before a leap day, and does not occur less than 50 years before any "missing leap day": that is, March 1st of a century-year which is not a leap-year. -- Don Reble djr@nk.ca
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Don Reble -
Thane Plambeck