[math-fun] September 10000, 1993
There's a bit of Internet folklore that says September 1993 never ended. (Look up "Eternal September" for details.) September 100, 1993 was otherwise known as Thursday, December 9th, 1993. September 1000, 1993 was otherwise known as Monday, May 27, 1996. September 10000, 1993 is today, otherwise known as Saturday, January 16, 2021. I thought about the pattern of the days of the week of the successive rollover days, and concluded that there's just one day of the week that they will never land on. Can you see which one, and why?
I'm guessing that anybody that has dived into calendar math for any time at all can figure this one out. I don't want to give spoilers, so I will digress a bit, with apologies to Keith. A vaguely related curiosity is that given dates of the year fall on the seven days of the week with *almost* equal probability -- almost but not exactly equal. This is because the central postulate of the Gregorian calendar is that 400 years equals exactly 146,097 days. Unfortunately, this period in days is exactly divisible by seven, so the day-of-the-week pattern in our calendar repeats exactly every four centuries. Calendar math is full of weirdness like this. I *still* haven't wrapped my head around the Hebrew calendar. The Islamic calendar is far simpler in principle, and (intentionally) full of mystery in practice. On Sat, Jan 16, 2021 at 5:01 PM Keith F. Lynch <kfl@keithlynch.net> wrote:
There's a bit of Internet folklore that says September 1993 never ended. (Look up "Eternal September" for details.)
September 100, 1993 was otherwise known as Thursday, December 9th, 1993. September 1000, 1993 was otherwise known as Monday, May 27, 1996. September 10000, 1993 is today, otherwise known as Saturday, January 16, 2021.
I thought about the pattern of the days of the week of the successive rollover days, and concluded that there's just one day of the week that they will never land on. Can you see which one, and why?
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If you haven’t seen it I’d highly recommend “Calendrical Calculations” by Dershowitz and Reingold https://en.wikipedia.org/wiki/Calendrical_Calculations?wprov=sfti1 Victor On Sat, Jan 16, 2021 at 19:21 Allan Wechsler <acwacw@gmail.com> wrote:
I'm guessing that anybody that has dived into calendar math for any time at all can figure this one out.
I don't want to give spoilers, so I will digress a bit, with apologies to Keith. A vaguely related curiosity is that given dates of the year fall on the seven days of the week with *almost* equal probability -- almost but not exactly equal. This is because the central postulate of the Gregorian calendar is that 400 years equals exactly 146,097 days. Unfortunately, this period in days is exactly divisible by seven, so the day-of-the-week pattern in our calendar repeats exactly every four centuries.
Calendar math is full of weirdness like this. I *still* haven't wrapped my head around the Hebrew calendar. The Islamic calendar is far simpler in principle, and (intentionally) full of mystery in practice.
On Sat, Jan 16, 2021 at 5:01 PM Keith F. Lynch <kfl@keithlynch.net> wrote:
There's a bit of Internet folklore that says September 1993 never ended. (Look up "Eternal September" for details.)
September 100, 1993 was otherwise known as Thursday, December 9th, 1993. September 1000, 1993 was otherwise known as Monday, May 27, 1996. September 10000, 1993 is today, otherwise known as Saturday, January 16, 2021.
I thought about the pattern of the days of the week of the successive rollover days, and concluded that there's just one day of the week that they will never land on. Can you see which one, and why?
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The Wikipedia article about the book doesn't dwell on geographic differences much. The Gregorian calendar was adopted at different times by various countries: IIRC, it was 1582 for Catholics, 1752 for England (& the colonies), ~1920 for Russia. Again IIRC, Knuth mentions a "no discontinuity" solution to the ~11-day gap problem, adopted by Sweden: omit Leap days for ~44 years. George Washington's birthday was February 11, 1731 Old Style, and became February 22, 1732 New Style. The English calendar reform also changed the start of the year from March 26(???) to January 1. This must be a mine field for historians. Rich --- Quoting Victor Miller <victorsmiller@gmail.com>:
If you haven?t seen it I?d highly recommend ?Calendrical Calculations? by Dershowitz and Reingold https://en.wikipedia.org/wiki/Calendrical_Calculations?wprov=sfti1
Victor
On Sat, Jan 16, 2021 at 19:21 Allan Wechsler <acwacw@gmail.com> wrote:
I'm guessing that anybody that has dived into calendar math for any time at all can figure this one out.
I don't want to give spoilers, so I will digress a bit, with apologies to Keith. A vaguely related curiosity is that given dates of the year fall on the seven days of the week with *almost* equal probability -- almost but not exactly equal. This is because the central postulate of the Gregorian calendar is that 400 years equals exactly 146,097 days. Unfortunately, this period in days is exactly divisible by seven, so the day-of-the-week pattern in our calendar repeats exactly every four centuries.
Calendar math is full of weirdness like this. I *still* haven't wrapped my head around the Hebrew calendar. The Islamic calendar is far simpler in principle, and (intentionally) full of mystery in practice.
On Sat, Jan 16, 2021 at 5:01 PM Keith F. Lynch <kfl@keithlynch.net> wrote:
There's a bit of Internet folklore that says September 1993 never ended. (Look up "Eternal September" for details.)
September 100, 1993 was otherwise known as Thursday, December 9th, 1993. September 1000, 1993 was otherwise known as Monday, May 27, 1996. September 10000, 1993 is today, otherwise known as Saturday, January 16, 2021.
I thought about the pattern of the days of the week of the successive rollover days, and concluded that there's just one day of the week that they will never land on. Can you see which one, and why?
_______________________________________________ math-fun mailing list math-fun@mailman.xmission.com https://mailman.xmission.com/cgi-bin/mailman/listinfo/math-fun
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participants (4)
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Allan Wechsler -
Keith F. Lynch -
rcs＠xmission.com -
Victor Miller