Re: [LEAPSECS] Telescope pointing and UTC

From: Steve Allen <>
Date: Thu, 30 Jan 2003 12:17:27 -0800

On Thu 2003-01-30T02:36:24 -0800, Ken Pizzini hath writ:
> Even if you
> assume that UTC will exist on past the life of the system, don't you
> expect that someday better DUT1 estimates will be available than the
> 0.1s signals available in WWV, and that future applications might
> find these better estimates to be useful?

The specifications for the automatic telescope call for an object to
appear within 10 arcsec of the field center after a slew. This is
congruent with what the telescope engineers can do with the flexure
and hysteresis, but it obviously requires UT1 good to about 0.66 s for
targets on the equator. Therefore we do need DUT1, but not to more
accuracy than it is provided. Higher cost telescopes may be able to
demand tighter specifications.

> And this once again brings me back to my perennial question: wouldn't
> it be more useful to the astronomical community for time broadcasts to
> include an approximation for sidereal-time-at-the-prime-meridian than
> an approximation of UT1?

It is already being done. The GPS constellation and the orientation
of the earth that it uses is expressed in an inertial reference frame.
By decree of the IAU, 30 days ago astronomers abolished the
three-millenium tradition of the Vernal Equinox in favor of an
inertial reference frame for all future astrometry.

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 Thu Jan 30 2003 - 12:17:38 PST

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