[g__day (Matthew)]

Folk I was wondering if this makes sense. If I drift align and calaculate how far an axis is from the refracted pole, can one simply use Jupiter's angular (equatorial) diameter of approx 50 arc minutes 2011/2012 as a good visual indicator of the correction amount?

Borrowing a formulea

Alignment Error (arc seconds) = arc tan(drift in arc seconds/(15*drift in time seconds)*360)/(2*PI) * 3600, e.g.

Drift arc seconds = 25 arc seconds (say 1/2 Jupiter's apparent diameter)
Drift in time = 3600 seconds
Polar misalignment error (arc seconds) =95.5 (a bit under two Jupiter diameters)
or Polar misalignment error (arc minutes) = 1.6



So if I centred the scope on Jupiter and it drifted to the edge - the scope was wandered about 1/2 of 50 arc seconds ~ 25 arc seconds. Let's say it took an hour to drift in DEC from Jupiter's centre to its edge - then from the above formulea I am 95.5 arc seconds or 1.6 arc minutes off the pole.

Expressed another way in that example I am just off twice Jupiter's diameter off the pole. So if I change the Alt or Az (as required) - using's Juptiers diameter as a guide stick - then I'd have a pretty neat frame of reference to polar align with.

Does this make sense to others - I have been searching for a visual means to guide me with what an arc minute or two looks like in my main OTA. Does approximating one Juptier diameter is 50 arc seconds at this time of year provide a simple measuring stick for fine tuning polar alignment?

Matt