>>2589532Yes, your telescope is rotating during these 20 minutes, to keep your object perfectly in the center of your field of view the whole time. The mount is compensating for earth's rotation, so nothing should move or be blurry, everything moves at the same speed in the sky. On long exposures, the only blurry things will be your foreground if you have one, and objects moving at different speeds than your starry background (planets, comets).
Everything else (stars, nebulae, galaxies) dont move relative to eachother, and thats very cool because you can take 500 frames one night, come the next day or week and take 500 more, and stack them together to increase your total exposure time.
As anon said above, imperfections in your mount or polar alignment will slowly make your stars move. The goal is to have the longest possible sub-exposures without having star trails. This number is usually around 2 minutes for amateur gear like mine. Autoguiding systems allow longer exposures. Its basically a camera pointing at a star, and sending small corrections to your mount when it detects that star moving 1 pixel to the left or to the right.
Again, stacking wont correct blurry images. You want your stars to be as sharp as possible on every sub-exposure. The goal of stacking is inceasing your signal (number of photons hitting your sensor to see fainter objects) and removing noise by averaging it out (camera/electronic noise, light pollution/skyglow etc)
sorry for poor englisherino
