On 08/11/2015 01:19 PM, Paul Gilmartin wrote: > On Tue, 11 Aug 2015 12:37:30 -0500, Joel Ewing wrote: >> >> Encyclopedia Britannica is complicit in the confusion to this day by >> incorrectly implying in their "Leap Year" entry that in addition to the >> divisible by 4, 100, 400 rules there either is or should be a 4000-year >> exception rule: >> "...For still more precise reckoning, every year evenly divisible by >> 4,000 (i.e., 16,000, 24,000, etc.) may be a common (not leap) year", >> >> Over 18 years ago (Nov 1996) EB acknowledged that no such rule exists: >> it was an un-adopted and sub-optimal suggestion by Sir John Herschel >> around 1820. EB has apparently not yet followed their own internal >> recommendation in 1996 "to reword this statement in the future". >> > If I were Emperor of the Universe, I would make the rule: > > Every year divisible by 4 except one divisible by 128 is a leap year. > > 365 31/128 is within one second of the mean tropical year; closer even > than the 4000-year rule. > > The unpredictable secular increase in the length of the day makes a > 4000-year rule pointless. > > -- gil >
Agreed. This is same view I have also had since 1996, but... Amazingly, if you do the math, the result of a 4/128 year rule is mathematically identical to the average days/year of a 4/100/400/3200-year algorithm. The 4/100/400 rule becomes about one day in error every 3200 years (the closest multiple of 400 years to the point where the error is 1 day), and since the Gregorian Calendar was adopted about 1600 (to the nearest century), years evenly divisible by 3200 turn out to be approximately the point where the error reaches 1/2 day and a reasonable point to start forcing a 3200-year correction to a 4/100/400 algorithm. Despite the elegance of a much simpler 4/128 solution, I would suspect there would be much less opposition to adding a 3200-year exception to the 400-year exception in the existing rules. The 19th-century proposal of a 4000-year exception would obviously have been a worse choice. All this presumes we or nature don't mess up the Earth's rotational speed too badly, convert to "stardates", or terminate civilization as we know it in the next 1200 years. -- Joel C. Ewing, Bentonville, AR [email protected] ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
