Part 4/11:
Hubble’s subsequent observations uncovered a critical relationship: the farther away a galaxy was, the faster it was receding from us, as evidenced by its redshift—a phenomenon where light stretches toward the red part of the spectrum. Plotting galaxy velocities against their distances revealed a proportional relationship, leading to the conclusion that the universe itself is expanding. In 1929, Hubble estimated this rate—later known as the Hubble Constant—to be roughly 160 km/sec per million-light-years. Although his initial estimate was refined over time, this provided a quantitative framework for understanding cosmic evolution.