Remove painted over glow in the dark stars?
Sounds like you're going to have to complicated-ly scrape those stars off! Seriously, though, you're right: it would take a fair amount of paint to stop the glowing, and even more paint to build up enough height to bury the stars completely.

The paint entombing the stars is most likely to be of the latex variety. This stuff is somewhat stretchy and rubbery, so to minimize peeling the paint away from the ceiling it'll be important to cut the paint around the star. Use a small and sharp hobby/craft knife to trace the outline of every star. Use light pressure -- you only need to cut through the paint film that's actually over the star, and it'll really be best if you can avoid damaging the paper facing of the drywall behind all the layers of paint.

With the perimeter of the stars cut free the next step is to lift them off the surface. You'll need some kind of prying tool. If the stars are just thin stickers then the knife itself may be adequate. If the stars are the thicker rigid plastic type then another tool may be better: a chisel, a putty knife, or some kind of scraping tool.

After the stars are gone you may want to make repairs. If the over-coat paint was thin and if the stars peeled away nicely then you might get away with just another coat of paint. On the other hand, if there's much of a step in the paint film or if there's damage to the underlying surface then you may need to use a filler like drywall joint compound or topping to smooth things. As in all drywall repair if you use a filler then you'll need to also use a primer before progressing to the new finish coat.