Whose Telescope Discovered the Expanding Universe?

In the 1920s, most astronomers believed the Milky Way was the entire universe. Edwin Hubble (1889-1953) changed everything. First, in 1924, he used Cepheid variable stars observed through the Hooker Telescope (then the world largest) to prove that the "Andromeda Nebula" was actually a separate galaxy millions of light-years away — demonstrating the universe was vastly larger than imagined. Then, building on Vesto Slipher redshift measurements and working with Milton Humason, Hubble showed in 1929 that the farther a galaxy is from us, the faster it is receding (Hubble Law: v = H0 * d). This was direct evidence that the universe is expanding — running the expansion backward implies a Big Bang origin. The "Hubble constant" (H0) quantifies the expansion rate and remains one of the most important numbers in cosmology. The Hubble Space Telescope, launched in 1990, was named in his honour.