Drift graph

[zerolatitude]

EW is East West, or RA. The image can have a steady unwanted movement, or drift, along this direction for several reasons, mostly to do with mount mechanics or periodic error.

NS is North South, or Dec. The image drifts along this direction generally because of polar alignment error.

There is a good explanation of this here http://www.minorplanet.info/ObsGuides/M ... gnment.htm

EW and NS are not up and down along the edges of the camera view. Instead the angle varies with where the scope is pointing, and the camera rotation. The image needs to be platesolved (or at least matched carefully with a star map), to determine which way is NS and which is EW. This is what the grid lines in the solved image tell you.

[Ancalime]

Thanks for yr tips. Hopefully a better image at next opportunity. Would 90s - 120s be doable, unguided on a skyguider pro?