Hey guys I been trying to figure out the location of various objects from a galatic perspective using celestia. One particular object that has been of help to me is the Horsehead Nebula. While doing this, I quickly realized that star's move, so a galactic map (if you could make one large enough) of all the major stars would be inaccurate in something like 500,000 years. However, this thought experiment has got me wondering. If star's move and drift around the galaxy with a set total velocity, do nebula's and gas clouds also have measurable velocities? A velocity besides their constant expansion? If they do move, how could one figure out the new Declination, Right Ascension, or any of the angular/distance coordinates of a nebula 100,000 sidereal years or some long time in the future? Is it a simple kinetmatics or dynamics problem using proper motion? Are there any tutorials that would help?