[AZ-Observing] Re: Troubles on the Pole [Was: Re: Re: Tonight (Friday)
- From: Stan Gorodenski <stan_gorodenski@xxxxxxxxxxxxx>
- To: az-observing@xxxxxxxxxxxxx
- Date: Tue, 27 Feb 2007 10:18:26 -0700
Jeff Hopkins wrote:
>Hello Stan,
>
>I never had any luck with the two star alignment. What I did was use
>the drift alignment to get the mount aligned and then each evening
>just point the telescope at a know bright star and then find the star
>on the key pad and sync it.
>
>Have you got the 16" Meade fine Polar aligned yet?
>
Instead of the drift method I'm going to try my own method I thought of,
although I am sure this has been thought of by other individuals. It may
even be in print. It is not suited for observing trips because of the
amount of time it takes, but it is suited well for my permanent setup
and is as follows.
I can get the transit times of Polaris at my location. Once I know this
I can determine the time Polaris will be at its north point, and its
east and west points. Then, say I start with the north point which, for
example, occurs at 10pm. At this point and time in the sky, Polaris has
a zero degree deviation in the east and west directions from the true
north pole (TNP). Since Polaris is 42 minutes of arc from the true north
pole I will not be able to get it and the TNP in the same field of view
with the telescope I have. However, that does not matter. All I have to
do is place my fork (rotate it) in the appropriate position so that I
can swing the OTA through the great circle that includes the Meridian.
Then I adjust my telescope azimuthally so that when I swing the OTA and
Polaris pops in view in the center of the field of view at some point in
the swing, I know the telescope is swinging along the great circle that
includes the Meridian. The telescope at this point deviates zero degrees
in an east-west direction from the TNP. Then I wait 6 hours, in this
example until 4am, and do a similar procedure for the altitude
adjustment. Because of the time it takes to make these adjustments,
Polaris will have moved from the respective E-W-N-S points and so I
would have to repeat this procedure the following night, possibly a few
more nights, to refine the adjustment.
One weak point with this method is getting the fork in the appropriate
position so that the OTA swings through the Meridian. I will use a
level, but this assumes the two axes are orthogonal to each other. I
think I can find out how far off they are by swinging the fork 180
degrees and seeing how far Polaris is from the center of the field of
view. Maybe I can add shims to bring them closer to orthogonality. Also,
I am assuming the center of the field of view in the eyepiece is very
close to the optical axis of the primary mirror. When I am done I will
use the drift method to see how good the alignment is.
Stan
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