The development of human awareness of the Universe evolved from the geocentric cosmology of the ancient world via the heliocentric cosmology of the Renaissance and the egocentric cosmology of the nineteenth century, to the ultimate destination of the Big-Bang theory of the expanding Universe.
In fabricating new constellations, puerility and meanness aided blind zeal in ransacking the heavens for amorphotae, or unformed stars, wherewith to wheedle accidental rulers of the hour, by exalting them and a heterogeneous assemblage of modern implements, among the heroes and classical symbols of remote ages.
There is a point of view among astronomical researchers that is generally referred to as the Principle of Mediocrity.... If the Sun and its retinue of worlds is only one system among many, then many other systems will be like ours: home to life. Indeed, to the extent that this is true, we should be prepared for the possibility that, even in the Milky Way galaxy, billions of planets may be carpeted by the dirty, nasty business known as life.
The evidence at present available points strongly to the conclusion that the spirals are individual galaxies, or island universes, comparable with our own galaxy in dimension and in number of component units.
Stating his conviction on the nature of nebulae during the Shapley-Curtis debate on 26 Apr 1920 to the National Academy of Sciences.