[LEAPSECS] Telescope pointing

[Steve Allen]

On Fri 2012-06-08T13:47:29 -0400, Gerard Ashton hath writ:

> So summarizing what I find in Steve's paper

[...]

> it requires intervention by the on-site observing technicians.

[...]

>  The same telescope will develop serious problems within a year of

> the discontinuance of leap seconds.


Different instruments on the same telescope have vastly different
fields of view in the acquisition/guiding.  The Shane 3-m is built
like a battleship, and points like a battleship.  The prime focus
camera has a huge FOV and pretty much can't miss.  The Coude focus has
a tiny FOV, and the skill of the telescope technicians is essential.


> This would suggest that when converting UTC to sidereal time, the older

> telescopes could ignore the distinction between mean and apparent Greenwich

> Sidereal Time.

> Probably even for the APF the subtle differences in the definition of

> Greenwich Sidereal Time that have been made in the last 30 years or so could

> be neglected, right?


Right.  (Truly it is a wonder to see someone actually recognizing the
nature of the difference between GMST and GAST.)  For observations of
the celestial sphere such a small (and non-secular)
celestial/terrestrial coordinate offset would get sucked into various
terms of the fit for the telescope pointing/flexure model.

Other telescopes manufactured like APF are intended for satellite
tracking applications.  We can lie to the configuration files and
still find celestial objects.  Satellite trackers cannot do that
because they depend on the correct transformation between celestial
and terrestrial.

--
Steve Allen                 <sla at ucolick.org>                WGS-84 (GPS)
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