A mathematical model that describes the distribution of stars within a globular cluster as a function of their distance from the cluster’s centre; also known as a King profile. The model uses two scales: a core radius, r_c, at which the density of stars as seen projected on the sky (and hence the cluster’s surface brightness) drops to half its central value; and a tidal radius, r_t , at which stellar density becomes zero. The King model is named after the American astronomer Ivan Robert King (1927– ), who first published it in 1966.