 For thousands of years, it was taken for granted that the universe was static. It always was, as we see it now, and it always will be. This was the case when Newton developed his gravitational equations. And it was the case when Einstein developed his general theory of relativity. Then, in 1929, Edwin Hubble published his studies of galactic velocities. He found that, except for a few nearby galaxies, all the spectra shifts were to the red. All of them were moving away from us. Here's what we see from galaxies in our Virgo supercluster, out to 100 million light-years. He discovered that the universe was expanding away from us. His Hubble law says that the further away a galaxy is, the faster it is receding away from us. The relationship is linear, a straight line, so the equation is simple. The receding velocity of a galaxy is equal to its distance times a constant, now called the Hubble constant. This constant has been refined over time and the distances used have increased by orders of magnitude using tools like the Hubble Space Telescope to analyze Type 1A supernova out to billions of light-years. The box at the lower left shows the region that Edwin Hubble probed. The current best value for the Hubble constant using this approach is 20.86 kilometers per second per million light-year. That is, the receding velocity of a galaxy goes up by almost 21 kilometers per second For each additional million light-years away from us, it is. This slow and steady movement of galaxies away from us is called the Hubble flow.