Transcript: The current expansion rate of the universe is given by the Hubble constant. Measurement of the Hubble constant was subject to an enormous effort over the past forty years culminating in the Hubble Space Telescope key project. In this huge collaboration involving hundreds of orbits with that precious facility, a series of measurements of the local universe involving Cepheid variables was used to derive the expansion rate. The answer was seventy kilometers per second per megaparsec with an error of only ten percent on that measurement. It’s still one of the most accurately measured numbers in cosmology. The expansion was shown to be isotropic, that is the same in different directions in the sky. The velocity of any galaxy predicted by the smooth expansion is called Hubble flow. However galaxies do not usually have exactly the velocity predicted by Hubble flow because gravitational interactions between galaxies cause them to depart from a smooth flow. The amount by which they depart is called a peculiar velocity. The average amount of peculiar velocities of galaxies in the local universe is about a hundred to a hundred and fifty kilometers per second.