Plot of the optical knots found by Fesen et al. (2008) in a radius-velocity diagram. The radius is the distance of the knots from the central pulsar projected to the plane of the sky, assuming a distance of 2 kpc for 3C 58. The observed absolute radial velocity is shown on the y-axis. The dashed line represents the outer edge of this distribution assuming no deceleration since birth and a connection to SN 1181. The dotted line represents the outer edge of this distribution for Sedov expansion (Sedov 1959) and a connection to SN 1181. The solid line represents the best-fit outer edge of this distribution.