Hi,
I do timelapse movies on comets sometimes.
If it's possible you can do a 1 point align on the comet core. The the star background will move. Or you can align on a star, the the comets move.
Fitswork is simple to use, I have a tutorial here and the software is free to download:
http://www.astrofriend.eu/astronomy/...-fitswork.html
An alternative is AstroImageJ, more difficult to use but have some advantages:
http://www.astrofriend.eu/astronomy/...roduction.html
Here is one example of a comet video, not very good, more a test:
https://www.youtube.com/watch?v=BJzy-aQJe30
/Lars