Hubble constant; (E.P. Hubble; 1925)

Definition: Hubble constant; (E.P. Hubble; 1925): The constant which determines the relationship between the distance to a galaxy and its velocity of recession due to the expansion of the Universe. After many years in which the Hubble constant was only known to be somewhere between 50 and 100 km/s/Mpc, it has been determined to be 70 km/s/Mpc ± 7 km/s/Mpc by the Hubble Space Telescope's Key Project team. (Advances in cosmology have shown that since the Universe is self gravitating, H_o is not truly constant. Astronomers thus seek its present value.)