[g__day (Matthew)]

Gary

Out of interest did your talk cover what path a star will travel through the sky? I expect most folk would say a circle, then change that on reflection to be an elipse (unless you're at the equator). But on further reflection - once you count in altitude and elevation based refraction - the path of a star across our night sky is likely to be a hyperbola.

So if a mount's controller realises that and models it correctly (mine uses King rates for refraction to compensate for this - as a function of elevation) how close to perfectly aligned can one come?

What I am saying is give a mathematican any spot on the Earth, including elevation - surely they could model the position of any star across the night sky down to the sub arc second if required (so long as they know the density of air above them and can ignore turbulence or large changes in air pressure systems). Once one factors in turbulence I imagine seeing can move a star +/- 1-2 arc seconds at sea level - does that sound right?


My mount did seems to show some hystersis - which I put down to slop in the DEC gears - probably about 15 arc seconds as a guess. But I don't see that this is the x-factor stymming my polar alignment when I am only watching the long term movement of a single star. I agree other factors such as the non orthorganality of any component in the mount / OTA system can cause pointing errors.

Cheers,

Matthew