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

From: Markus Kuhn <Markus.Kuhn_at_cl.cam.ac.uk>
Date: Tue, 08 Jul 2003 10:54:32 +0100

A point that was made repeatedly at Torino is that the term "UT"
traditionally meant in astronomy a time scale defined by the Earth's
rotation, and that therefore a leap-second free uniform atomic time
should not be called UTC, even if doing so would of course avoid the
need to change the large number of national regulations that explicitely
refer to "UTC" today.

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?

I always thought it was a rather odd selection of words:

"Universal Time" is not linked in any way with the "Universe" as such.
It is related to the position of the sun in a coordinate system that is
attached to the crust of this particular piece of molten rock.

Wouldn't "Terrestrial Time" have been the obvious choice, to clarify
that this time is tightly linked to this planet?
(The term "Terrestrial Time" is today unfortunately already used of
course for the modern geocentric replacement of ephemeris time.)

The laws of gravity (ephemeris time) and quantum physics (atomic time)
on the other hand are presumably properties of the entire universe, and
therefore any time scale that attempts to approximate the physical
passage of time (TAI, or one of the equivalents in a less earth-bound
coordinate system, e.g. barycentric) would perhaps much more deserve the
name "Universal Time".

The entire astronomical and radio communications time terminology has
gradually evolved into quite a mess that ought to be sorted out from
scratch. Not to mention the odd semi-French semi-English acronyms.

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 that isn't crippled by historic accidents but is
designed to be a real pleasure to teach in an introductory physics,
astronomy or computer networking class to new students. Why stick with a
badly evolved terminology that originated before we had general
relativity, ephemeris and atomic time?

[Yes, I know how difficult it is in our committee-driven world to
redesign a standard properly from scratch, as opposed to the easier path
of continually adding on little bits while minimizing short-term
controversy over backwards compatibility.]



Markus Kuhn, Computer Lab, Univ of Cambridge, GB
http://www.cl.cam.ac.uk/~mgk25/ | __oo_O..O_oo__
Received on Tue Jul 08 2003 - 02:54:51 PDT

This archive was generated by hypermail 2.3.0 : Sat Sep 04 2010 - 09:44:54 PDT