Re: [LEAPSECS] Is Julian Date a time or an Earth angle?

From: Markus Kuhn <>
Date: Fri, 04 Jul 2003 10:32:51 +0100

Steve Allen wrote on 2003-07-03 18:09 UTC:
> 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.

"Elapsed time" ("time" in the sense of ephemeris time or atomic time)
would actually be easier to calculate, at least if you used a Julian
Date derived from real time, not UT. What does become more difficult to
calculate is the elapsed rotational angle of the rock on which we live.
But I suspect that people who need to do that will find it easy to get
access to TI -> UT conversion tables for this planet.

As someone from the BIPM stressed at the Torino meeting, we shouldn't
forget that UT isn't really a measure of time. It is merely the angle of
a mass in the solar system that was historically used as one popular
practical representation of time. Another ancient practical
representation of time has been the longitude of the sun, which we now
know happens to be a far more long-term stable measure.

> 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?

I'm not too worried. If you want to have an additional Friday on your
CV, just book a cruise around the world eastwards. Money can buy you a
day, and even the poorest soul can affort it once every ~3000 years.

People interested in religions had to adjust over the past few hundred
years the technical details of their views and teachings many times to
match our increasing understanding of the physical world. The
reinterpretation of ancient algorithms for scheduling religious rituals
in the light of advances in timekeeping should be a stimulating
intellectual exercise for these communities and not a cause for war. Any
omnipotent god surely will be delighted if his subjects learn to pray
with ultimate precision scheduled by a quantum mechanics timescale. May
be, it is just another step towards theological perfection?


Markus Kuhn, Computer Lab, Univ of Cambridge, GB | __oo_O..O_oo__
Received on Fri Jul 04 2003 - 02:33:05 PDT

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