Re: "Universial" Time, "Terrestrial" Time -- time for new terminology?

From: Steve Allen <>
Date: Tue, 8 Jul 2003 09:06:26 -0700

On Tue 2003-07-08T10:54:32 +0100, Markus Kuhn hath writ:
> I understand that the term "Universal Time" was cooked up in the IAU in
> the 1920s, but does anyone know more details about the origin of and
> reasons for this curious choice of terminology?

It's all laid out in plain French and English in the Transactions of
the IAU from 1925 and 1928. It is tied up with the decision that,
contrary to Newcomb who started the day at noon, all national
ephemerides should change to reckon the day as starting at midnight.

It is also tied up with the stubbornness of the publishers of the
British almanac who, despite pleas from everyone else, refused to
adopt a new term for time starting at midnight. So, in the British
almanacs before 1925 GMT means "starting at noon" and after 1925 GMT
means "starting at midnight". From the transactions you can infer
that the delegates spent so much time arguing with the British about
GMT that they never had time to consider choosing a common name for
the new "earth rotation timescale reckoned from midnight".

By 1928 that was partly remedied by agreeing on three synonymous
terms: Universal Time (U.T.), Weltzeit (W.Z.), and Greenwich Civil
Time (G.C.T.). The seasonal fluctuations of UT were not known for
another decade, and it was not until the 1950s (when ET was already
under consideration) that the almanacs actually started using the term

> "Universal Time" is not linked in any way with the "Universe" as such.

Catholic doesn't mean what it used to either, but not even l'academie
francaise can keep the people of a single country from doing those
sorts of things to their language.

> Wouldn't "Terrestrial Time" have been the obvious choice, to clarify
> that this time is tightly linked to this planet?

If you were going to rewrite it all now, you might want Crustal
Rotation Time. After all, the old meaning of CRT is fading away.

> If we fiddle with the definition of UTC, wouldn't this also be a good
> opportunity to finally draw up a simple, clear and logic terminology for
> time scales?

One problem is doing this without (as the British almanac did)
introducing an ambiguity in the meaning of any term that is already in
use. Unlike the internet, the scientific unions of the world do not
have an official IANA-like body to control the technical namespace.
Another problem is that creating new names for concepts that
are already in use has collateral damage on all the other
legal codes and standards that cite those concepts.

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 Tue Jul 08 2003 - 09:07:33 PDT

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