From: Mark Holm 
To: atm{at}shore.net, tkrajci{at}san.osd.mil
Reply-To: Mark Holm 


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{at}telerama.com

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