In 1950 he became an assistant to E. P. Hubble, whose work on measuring the distances of galaxies and refining the value of the Hubble constant he continued, finding a value of around 50 km/s/Mpc. He also calculated an early value for the deceleration parameter. In 1960 he and the Canadian astronomer Thomas Arnold Matthews (1927– ) made the first optical identification of a radio source (3C 48) that would turn out to be a quasar. In 1965 Sandage found the first radio-quiet quasar, and went on to identify many more quasars by their high redshifts.