SV: ATM Adjusting RA Tracking Rate Question

["Nils Olof Carlin" <nilsolof.carlin@telia.com>]

Al,

>Gerald North, in his book Advanced Amateur Astronomy (Cambridge), says....
>an altitude error in the polar axis produces an East-West drift which is
>greatest for objects near the meridian. An azimuth polar axis error produces
>an East-West drift that is greatest for an object at 6h East or West of the
>meridian. 

A back-of-the-envelope calculation gave (no guarantee given;-) a N-S drift of 
15.7*cos(declination) arcmin per degree error of the polar axis and per hour - at +-6h 
for an error in altitude and at the meridian for an azimuth error (or rather at right 
angle to the meridian). The E-W error at the meridian per degree error at the meridian is 
15.7*sin(declination) arcmin per degree error and hour.

So if you do the polar adjustment by minimizing the N-S drift at the meridian and at + or 
- 6h (I expect you did) and then measure the E-W drift for a star near dec 0 (as you said 
you did), the polar axis error should make a very small contribution.

>So, my approach has been to do the best polar alignment I can (drift
>method), then set the RA rate by tracking a star, then going back and doing
>another polar alignment, then re-adjusting the RA rate again by star
>tracking, then ..... and so on.

I would have thought that unless the RA rate is so badly off that you lose the star (east 
or west) in a short time, you needn't bother about adjusting the rate until you have the 
polar axis adjusted as best you can by minimizing N-S drift (that is if you can 
distinguish clearly between N-S and E-W drift!).

Nils Olof