The Expanding Universe

Abstract

In the 1920s, Edwin P. Hubble discovered that distant galaxies were all moving away from the Milky Way. Not only that, the farther away he observed, the faster the galaxies were receding. He found the relationship that is now known as Hubble's Law: the recessional velocity of a galaxy is proportional to its distance from us. The equation is: v = Ho × d, where v is the galaxy's velocity (in km/sec), d is the distance to the galaxy (in megaparsecs; 1 Mpc = 1 million parsecs), and Ho is the proportionality constant, called "The Hubble constant."