The Faber-Jackson relation is an observed correlation between the random speeds of stars in the center of an elliptical galaxy and the intrinsic luminosity of the galaxy – the higher the random speeds, the more luminous the galaxy. Since the speeds of stars can be directly measured by the Doppler shift in their spectra, the Faber-Jackson relation gives a way of estimating an elliptical galaxy's intrinsic luminosity. By comparing this with the observed brightness, the distance to the galaxy may be inferred. It is named after the American astronomers Sandra Moore Faber (1944–) and Robert Earl Jackson (1949–). See also the Tully-Fisher relation, which is applied to spiral galaxies.