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Sept. 2, 1752 was a Wednesday. Adding fourteen days (two weeks), can you figure out what day of the week Sept. 16, 1752 was?
Halloween falls on a Saturday this year. July 4 next year will be on a Sunday.
If you own a perpetual calendar, you can look these dates up.
But without having a calendar handy, could you determine on what day of the week Valentines Day falls next year? Or Christmas? Your birthday? Uh, okay ... how about Easter Sunday?
It’s actually pretty easy to figure out these dates in your head and I thought it might be fun to write up the technique for anyone who might want to learn it.
The algorithm for calculating days of the week for a given date is called the Doomsday Algorithm. Why they didn’t call it the “Calculate Day of the Week Algorithm,” I can’t say. I prefer to just call it the D-day algorithm.
Let’s see how this works for the years 2009 and 2010. You rarely need to know the day of the week for any date more than two years out.
First, we define “D-day.” For any given year, the day of the week on which the last day of February falls is the D-day for that year.
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