[ngcles]

Hi Peter,

P.A (or position angle) is the number of degrees east of north the secondary star is from the primary. So PA 90 is due east, PA 180 is due south and PA 270 is due W.

So the distance in arc-seconds describes the size of the gap between the stars and PA describes the direction from the primary (brighter) and the secondary.

I don't know how you 'scope is mounted (eq of alt-az) but if it is an equatorial (assuming it is roughly aligned at least), your drive motors will move the 'scope in those 4 directions -- NSEW, so you can then estimate the PA. This of course is a bit trickier in an SCT used with a star diagonal and leaves you with a mirror-reversed image, but it can be done. It is harder still if the 'scope is mounted alt-az and its directions of motion don't line up with the cardinal directions. The best you can do (as you look through the ep) is to push it directly as possible toward the SCP. The direction new stars enter the field of view is approximately south and you can work the other directions out from there (taking into account the orientation of the view ie Mirror reversed, inverted, bot, etc etc.).

For extended objects like a galaxy, we only use the PA degrees between 0 and 179. A galaxy in PA 0 is lengthened (ie the major axis is elongated) exactly north-south. PA 45 is northeast-southwest, PA 90 is east-west etc etc. Obviously enough the angles between 179 and 359 are redundant and so not used.

Hope this helps.

Best,

Les D