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[Warner Losh]

On Aug 9, 2013, at 9:17 AM, Rob Seaman wrote:


> On Aug 9, 2013, at 4:34 AM, Gerard Ashton <ashtongj at comcast.net> wrote:

> 

>> Leap day implementation doesn't seem to do so well in years evenly divisible

>> by 100. Also the choice of Julian or Gregorian calendar is related to leap

>> days, and keeping track of which country (or subdivision thereof) switched

>> on which date is dumped upon the end user.

> 

> And even though the implementation remains imperfect, neither Julian nor Gregory proposed doing away with leap days and pretending that the year is an integral number of (solar) days.


Julian was set in stone in 46BC, so people have been adding leap days every 4 years for 2000 years. They had been doing it every 4 years for 1600 years when the Gregorian calendar came along. Although the definition was set in 46BC, the Julian calendar got off to a rocky start, by having every 3rd year instead of every 4th year have the leap day (due to counting inclusively instead of exclusively). After 36 years, this meant that 3 too many days had been inserted, so they stopped leap days for about 16 years to catch up (the ancient sources conflict on the details, but wikipedia has a nice table).

Gregorian was promulgated by Pope Gregory in 1582, but it wasn't until 1928 that all the major countries of the world had adopted it. The slow roll out of the calendar has many amusing anecdotes associated with it (not least is February 30, 1712 in Sweden). It took the world about 350 years to get on the same page. And even today the Orthodox Church has refused to adopt it, calculating all its holy days on the more traditional Julian calendar (although some parts of the Orthodox Church keep records in whatever the local calendar is at the time). And some parts of Africa still use a variation of the Julian calendar for their civil time.

There have been many proposals to unify the two calendars, by creating a 'reformed Julian' calendar that agrees with the Gregorian calendar for the next eight hundred years. This was at an Orthodox synod in 1924, but has been universally ignored by the Orthodox church.

So given then bumpy history of calendar reform, it should surprise nobody that some 40 years into this leap second experiment we're having problems still... Especially since the method of insertion of leap seconds still is observational rather than formulaic, a throw back to the pre-Julian practice of adding or subtracting time to make the dates line up.

Warner