Astronomers characterize the morphology of a globular cluster by means of standard radii. These are the core radius ("r""c"), the half-light radius ("r""h"), and the tidal (or Jacobi) radius ("r""t"). The overall luminosity of the cluster steadily decreases with distance from the core, and the core radius is the distance at which the apparent surface luminosity has dropped by half. A comparable quantity is the half-light radius, or the distance from the core within which half the total luminosity from the cluster is received. This is typically larger than the core radius.