Hubble Discovers the Expanding Universe

In 1929, American astronomer Edwin Hubble published observations showing that distant galaxies are receding from us at velocities proportional to their distance — now known as Hubble's Law. This discovery, made using the 100-inch Hooker telescope at Mount Wilson Observatory, provided the first observational evidence that the universe is expanding. The finding confirmed predictions from Einstein's general relativity and Georges Lemaître's earlier theoretical work. It revolutionized cosmology and eventually led to the Big Bang theory of the origin of the universe.