Re: [LEAPSECS] Telescope pointing and UTC, was: Re: What I do. What do you do?

From: Steve Allen <>
Date: Wed, 29 Jan 2003 23:55:26 -0800

On Wed 2003-01-29T22:14:35 -0800, Ken Pizzini hath writ:

> You lost me on this: you require sub-second UT1, which means that
> you have some means of inputting either UT1 or UTC-UT1 besides
> feeding in the standard time broadcasts.

The standard time broadcasts contain estimates of DUT1, the difference
between UTC and UT1, to an accuracy of 0.1 s. See

The GPS frames contain the information needed to compute DUT1, but
not a direct estimate as the shortwave signals do.

Mark Calabretta just mentioned an operational system using another
means of getting DUT1, which is to scrape it off the web pages of the
earth rotation agencies.

It is our presumption that the contractor delivering this new
telescope will choose one of these means in order to meet the pointing
accuracy specifications, but at this stage we do not know which means
will be chosen.

> Why would the means of
> injecting this input be tightly integrated with the observing
> programs, rather than designing the obeserving programs to take
> a declaration of "this is my best effort at UT1" as input, and
> having a thin, readily replaced, interface doing whatever translation
> it is that you need to do with UTC (as it exists now) to give you your
> sub-second UT1?

I have no idea what this question is asking.

In order to point the telescope accurately it is necessary to know the
sidereal time, and that is computed directly from UT1 and the
longitude of the telescope.

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 Wed Jan 29 2003 - 23:55:37 PST

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