Quote:
Originally Posted by xelasnave
I even thought that say imaging an object in the South that via this system I could select a faster moving star in the North which I would think should provide advantage.
Why won't this idea work?
Alex
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Hi Alex,
The effect of refraction is to "lift" objects in altitude.
The amount of lift from refraction is a non-linear function of the star's zenith distance.
At the horizon, refraction is the greatest, causing an apparent lift of about
half a degree.
At 45 degrees zenith distance, the lift is a couple of arc minutes.
At the zenith itself, it reaches zero.
So for two stars that have different zenith distances, their apparent angular
separation is continuously changing as a function of time as the Earth rotates.
Their instantaneous tracking rates are also continuously varying and are not
the same.
So if you choose a guide star that has an appreciably different
zenith distance to the target and the exposure is long enough, your image
will have trails.
For the same reason, there is no such thing as a "perfect polar alignment".
There are only compromises. Equatorial mounts are an engineering kludge
to help minimize field rotation, not a perfect solution.
Best Regards
Gary Kopff
Managing Director
Wildcard Innovations Pty. Ltd.
20 Kilmory Place
Mount Kuring-Gai NSW 2080
Australia
Phone +61-2-9457-9049
Fax +61-2-9457-9593
sales@wildcard-innovations.com.au
http://www.wildcard-innovations.com.au