Re: [LEAPSECS] Unifying Atomic Time and the post-Gregorian calendar corrections

From: Steve Allen <>
Date: Thu, 3 Jul 2003 11:09:31 -0700

On Thu 2003-07-03T18:30:00 +0100, Markus Kuhn hath writ:
> Thanks for pointing this out! Weekday-continuity is indeed a bit of a
> problem of this approach. I can't see any other practical solution than
> skipping one weekday together with the skipped 29 February 5600, in
> other words, 5600-03-01 would be a Wednesday also in all the local
> civilian time zones.

It also deserves to be pointed out that the Julian Date would not
match in the two different calendrical schemes. With that it becomes
tricky to calculate elapsed time.

> But then, they didn't have computer software to worry about during any
> of the past calendar reforms. I think user requirements might have
> changed for weekdays.

Are you willing to risk a fatwah if this is implemented and you are
identified as the one who proposed that a Friday will eventually
disappear from the calendar?

> According to
> astronomers such as John Herschel (1792-1871) and others suggested in
> the past to augment the Gregorian calendar with a rule that makes every
> year divisible by 4000 not a leap year. Similarly, the Orthodox church
> in Greece considered in the 1920s to replace the Gregorian "Y mod 400 =
> 0" rule with a "Y mod 900 in {200, 600}" rule. I'd be curious to hear,
> whether the usefulness of such proposals have ever been discussed more
> recently in the light of modern astrometric and orbital-modeling
> capabilities. Or do we first have to build a vast solar-system wide
> equivalent of GPS to gather data about the solar gravitation and
> pressure environment with sufficient accuracy for long-term forecasting?

Read the reference near the bottom of my Future of UTC page:

Newcomb's mean longitude of the sun includes terms which naively
appear to be secular but which are actually the leading wave of
periodic changes. That is why they should not be used even now, let
alone a long time from now. Herschel did not have access to anywhere
near as many or as accurate a set of obsesrvations as Newcomb did.
There is no way to take Herschel's long term prediction for the
calendar seriously.

The deceleration of earth rotation is a secular term which we can be
sure will affect civil time. On the contrary, I would be very
surprised to find anyone who would seriously contend that there are
any secular changes of the earth's orbit or obliquity which are
predictable enough to justify complicating the SRG's business.
Nevertheless, I'll ask around just to be more sure.

Steve Allen          UCO/Lick Observatory       Santa Cruz, CA 95064      Voice: +1 831 459 3046
PGP: 1024/E46978C5   F6 78 D1 10 62 94 8F 2E    49 89 0E FE 26 B4 14 93
Received on Thu Jul 03 2003 - 11:09:42 PDT

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