Re: ATM Alt-alt telescope mount - and image rotation

["Dwight K. Elvey" <dwightk.elvey@amd.com>]

>From: "Mark Holm" <mdholm@telerama.com>
>
>Tom,
>
>I still don't know the equations, but here is a strategy.
>
>Pick two convenient points in the alt-alt coordinates.  For example, make one 
of 
>the coordinates exactly the same for both points.
>
>Transform those points into equatorial coordinates.
>
>Rotate the points some amount, perhaps 15 degrees (1 hour) in hour angle.

Hi
 As I mentioned earlier, It doesn't rotate at a constant rate
over time. Knowing the end points doesn't tell you what instantaneous
rate it should use. This only give you the average rate.
Of course, a little calculus here would work.
Dwight

>
>Transform the points back into alt-alt coordinates.
>
>Determine the rotation difference between the first and second set of alt-alt 
>coordinates.
>
>Now I am not sure exactly how to define the last step.  The two transformations 
>should be doable by a standard set of instructions to be found in a spherical 
>trig book, or perhaps on the web.  It should be the same as the conversion from 
>alt-az to eq except that some of the numbers will be different.  Remember that 
>and alt-alt is just an alt-az that has been translated, without rotation to a 
>different point on the earth.
>
>In fact, that may be the easy way to fake this problem.  Just work out the 
place 
>on earth where your alt-alt would be an alt-az and use the equations that apply 
>to the alt-az case for that location.  If your alt-alt is aligned north-south, 
>the appropriate place would be 90 degrees different in latitude.  If it is 
>oriented east-west, it would be 90 degrees in longitude.
>
>Mark Holm
>mdholm@telerama.com
>
>
>
>