[LEAPSECS] Telescope pointing

[Warner Losh]

On Jun 8, 2012, at 9:51 AM, Rob Seaman wrote:


> On Jun 8, 2012, at 8:26 AM, Gerard Ashton wrote:

> 

>> There seems to be confusion between the preprint table of contents and the

>> titles of the papers one finds upon clicking the link. Could you specify how

>> to get to the preprint?

> 

> 

> I think Steve meant:

> 

> 	http://www.cacr.caltech.edu/futureofutc/preprints/38_AAS_11-678_Allen.pdf

> 

> The whole list of preprints are reachable from:

> 

> 	http://www.cacr.caltech.edu/futureofutc/preprints/

> 

> Note that a UT1 correction is only part of the issue.  Many telescopes and other systems make the natural assumption that UTC itself approximates Greenwich Mean Time, since the original TF.460 was created with this in mind:

> 

> 	"GMT may be regarded as the general equivalent of UT."


Allen's paper goes into how much various telescopes rely on this, and how much adjustment can be made to their timing base.  Some have timing systems that can be swapped out (at considerable expense, most likely) which could be used to correct should DUT1 exceed 1s, but many do not (IIRC, I've heard of some with built-in GPS receivers to get time, and the internal receivers were hard to swap out, and GPS signals are difficult to generate in real time).

Warner