Evolution of the radius (top panel) and instantaneous apparent opening angle (bottom panel) of the jet in M 87 with distance from the core. A power law fit to the jet radius is consistent with results obtained by Asada & Nakamura (2012; dashed line) and Hada et al. (2013; dashed dotted line). Evolution of the instantaneous opening angle corresponding to the power law fit obtained for the jet radius is shown by the solid gray line in the bottom panel.