 For the longest time it was not known whether stars like these shined by their own light or whether they were reflecting the sun's light as all the planets, moons, comets and asteroids do. It's only in the last couple of generations that we have finally reached a point where we know what stars are. You'll recall that Copernicus first proposed a sun-centric model for the solar system, but you'll note that the outermost celestial sphere did not go away with the Copernican model. Parallax measurements showed us that the sun was at the center of our planetary system, but no one could find any parallax in the stars, not Tycho Bra, not Kepler, not Galileo, not even Newton. The reason it took so long is that stars are so very far away that parallax angles are just too small for the available instruments. Remember that the moon's parallax was one half of a degree, but star parallax is measured in fractions of an arc second.