Re: [LEAPSECS] floating prime meridian

From: Michael Deckers <>
Date: Thu, 31 Aug 2000 10:47:52 +0200

   Rob Seaman wrote:
> This mailing list has been so quiet that I actually reread one of my
> own messages - and found this erroneous passage:
> Note that currently UTC is tied to the location of the prime
> meridian. One interpretation of a floating UTC is a floating
> prime meridian. We may be generating a vast market for surveyors
> in Great Britain over the next century as the meridian moves a
> couple of miles east of the Airy Transit Circle.
> (Or is it west? Quick! Which way?)
> The estimate is that UTC will diverge from UT1 by about 140 seconds over
> the next century. That's two minutes of time, but about 35 minutes of arc.
> At the equator a minute of arc is a nautical mile. At the latitude of
> Great Britain, 140 seconds of time is about 20 miles.
> The final question remains, however. Which way does it move? If it's
> hard for us to have complete confidence in sorting out this not entirely
> pedagogical question in our own heads - should we be generating a
> situation in which laypeople (bilyuns of 'em) would have to invert
> the process in the future?
> Rob Seaman
> National Optical Astronomy Observatory

   The concept is known in astronomy under the name of ephemeris meridian
   (using terrestrial time TT instead of the proposed "floating UTC").
   See eg the web site "".
   The ephemeris meridian is nowadays east of the prime meridian, which,
   incidentally, is no longer defined by the Airy Transit Circle.


   Michael Deckers email:
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Received on Thu Aug 31 2000 - 01:56:51 PDT

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