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

[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.

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