Re: APPC RA rate

Roland Christen

You can make the RA drift either slower or faster by raising or lowering the altitude axis. There is a point where the drift rate at the zenith is exactly zero. The RA will of course drift slightly as you move away from the zenith in any direction, and this is caused by the well-known atmospheric refraction effect. Thus there is no one setting of RA tracking rate that works everywhere in the sky, but can work nicely within +- 1 to 2 hours from the zenith.


-----Original Message-----
From: craig.young.m8@... [ap-gto]
To: ap-gto
Sent: Fri, Aug 25, 2017 1:27 am
Subject: RE: [ap-gto] APPC RA rate

Hi Howard,

I am not familiar with using a star at the zenith for altitude adjustment.  Can you point me to a reference on how this is done.  For instance, how sensitive is the method to selecting a star that is not exactly at the zenith.  Or, can plate solving be used to determine the drift, e.g., move the scope to HA -10 minutes, take an image and solve, then 10 minutes later another image and solve, measure the drift, adjust the altitude and repeat as necessary.

And a quick note, I did get some clear weather last night and did a 30 point APPM model of the eastern sky.  I then used APPM model to set the tracking and it worked very well.  Previously, with the altitude off by a couple of degrees, the APPM model did not work for tracking, so it appears to be sensitive to this.  With the new alignment it works much better.  So the emphasis now is to tighten up the alignment to less than an arc minute in both axis.


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