Modern astronomy began when Harlow Shapley went to Mt. Wilson Observatory in 1914, to study globular clusters. He determined that our solar system was located far from the Milky Way's center, 2/3 the way toward the rim. Shapley was wrong in thinking spirals like Andromeda (M31) were inside our Galaxy.
Enter Edwin Hubble! He was arrogant, a boxer. He liked to be photographed smoking a pipe. He went to Mt. Wilson after fighting in World War I. He and Shapley hated each other.
Hubble concentrated on galaxies, which were called "spiral nebulae." Using the 100-inch telescope, he concluded that M31 and other spirals were beyond our Galaxy.
The expanding universe came next! Hubble discovered that galaxies were moving away from each other and that the farther away they got, the faster they receded. The universe was expanding like a balloon! Timothy Ferris titled his book after the redshift seen when the Doppler effect is applied to light.
Ferris gets into cosmology. He says that neither a finite universe nor an infinite universe explains things. He proposes "a finite but unbounded universe" (whatever that means). Einstein introduced the concept of a space/time continuum but had trouble accepting an expanding universe. The 200-inch at Mt. Palomar opened new vistas. Astronomers photographed galaxies and looked back in time. Walter Baade and Milton Humason contributed.
It became clear that the galaxies were once compressed in a single point. Georges Lemaitre called it the "primeval atom." George Gamow championed the idea.
Fred Hoyle coined the term "Big Bang" as a put-down because he advocated the Steady State theory.
We know the universe is expanding, but will its expansion continue? It appears now that it will. The universe will die!
Cosmologists speak of a mulitverse. It may be that our universe is but one of an infinite number of universes. There may be an infinite number of Big Bangs.
Ferris hints that our cosmology will one day be as antiquated as the cosmology of Ptolemy.