Colby Gutierrez-Kraybill wrote:
I love following the broad tangents that come up on this list...
I wanted to chime in on observatory use of sidereal time, and guider
scopes, etc... At the research class instrument level, as is being
pointed out (har har), pointing models are heavily used, for both
first acquiring a source and more importantly to ensure that tracking
the source is steady across the period the telescope is taking data.
Minimising the error that an autoguider or similar device has to deal
with is conducive to better tracking.
Second, guider scopes in radio astronomy seem to be rare. The uses
I'm aware of are usually used for coming up with accurate pointing
model coefficients, by pointing at dozens of mag 1-6 stars all across
the sky periodically. How often that is done depends on how stable
the mounts of the telescopes are. For many radio telescopes, having a
bright enough source in or near the field of view is rare enough to
put it very low down on a priority list of control elements. Not to
mention they're not much use in bad weather conditions that are
otherwise okay for the frequency ranges a given radio telescope
operates at, nor during the day, where even though you can see stars
with proper filters, you're even more limited on how many you can see.
For our day-to-day use, sidereal is only used as a reference for
knowing approximately what RA is up at that moment, which makes a
visual sidereal display very useful.
Most large optical telescopes (eg MMT) don't seem to use classical
finder or guide scopes.
A classical guide scope doesnt work well with 20th magnitude objects as
its aperture just isn't large enough.
Using an eyepiece with a large telescope is problematic at best.
Usually an acquistion camera with a limited field of view is used instead.
Bruce
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