Copernicus deflated human egos by pointing out that the Earth is not the center of the Solar System. Shapley deflated our egos still more by pointing out that the Solar System is not the center of the galaxy. After long debate, it was shown that our galaxy is one of billions of other galaxies. Through a small telescope, the Andromeda Galaxy looks like yet another faint, fuzzy patch, like the Orion Nebula, the Ring Nebula, or the Crab Nebula. For many decades, there were two viewpoints on the nature of spiral nebulae.
Spiral nebulae are disk-shaped galaxies like our own.
The nearest spiral nebulae are 10 kpc across and 1000 kpc away. Spiral nebulae are swirling gas disks within our own galaxy. The nearest are only 1 pc across and 100 pc away. The debate was resolved by Edwin Hubble in 1924. The Cepheid stars were apparently very faint, which meant that the Andromeda Nebula was outside our own galaxy, and constituted a galaxy of its own.