To: atm{at}shore.net
From: MLThiebaux 
Reply-To: MLThiebaux 


Here's a formula for this rotation rate:

We can think of this system as an equatorial mounting with the polar axis
grossly misoriented.  Say the polar axis is pointing at a fixed point T in
the sky with declination  t. (If Dobsonian, read azimuth axis instead of
polar axis).

Suppose we are tracking a star with declination  s.  Let  H  be the hour
angle of the star minus the fixed hour angle of T.  H is increasing at the
constant rate  w = 15 deg/hr.

Let A = cos(s)tan(t)  and   B = sin(s).
Then the apparent rotation rate in the field of view of the telescope is

        w(B-AcosH)/[(sinH)^2 +(A-BcosH)^2)].

Note that the rate is time-varying; a positive rate corresponds to a
counter-clockwise rotation in a 2-mirror telescope.

Martial Thiebaux
Rawdon Hills, Nova Scotia

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