Re: [LEAPSECS] two world clocks AND Time after Time

From: Markus Kuhn <Markus.Kuhn_at_CL.CAM.AC.UK>
Date: Mon, 24 Jan 2005 09:23:48 +0000

Steve Allen wrote on 2005-01-24 06:09 UTC:
> But the current strategy of retaining the name UTC creates one real
> and unresolvable problem that will persist indefinitely. It is very
> bad policy to corrupt the historical meaning of anything called
> "Universal Time" by redefining UTC to be something that has no
> relation to the rotation of the earth.

It has been historically rather bad terminology to start with, so I
wouldn't shed too many tears here.

"Universal Time" sounds to me like a more suitable name for a time scale
that is linked to a property of the entire known universe, say a
frequency defined by the electron configuration of the caesium atom.

"Terrestrial Solar Time" would have sounded like a *far* more fitting
name of a time scale that is linked to Earth's rotational angle.

Unfortunately, astronomers chose their terms exactly the wrong way round
in a counter-intuitive way, where "Terrestrial Time" is actually a
physical time scale and "Universal Time" is an Earth angle time scale.
Of course, relativity tells us that there is no such thing as a
"Universal Time", and that we have to attach any time scale to some
coordinate system (e.g., barycenter of sun or earth).

It would be nice to have a more streamlined terminology, where
individual words/letters in the acronyms unambiguously indicate

  - whether the time is physical (counting SI seconds) or solar
    (defined by the position of the mean sun relative to a body
    in the solar system)

  - if it is physical time, where the relativistic reference frame
    is attached (barycenter of the milkyway, sun, or some planet,
    or the surface of some planet)

  - if it is a solar time, which planet and how is the prime
    meridian defined

  - if it is a solar time, which periodic deviations have been removed


Markus Kuhn, Computer Lab, Univ of Cambridge, GB | __oo_O..O_oo__
Received on Mon Jan 24 2005 - 01:24:00 PST

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