When a star has a bright outburst, the light may illuminate clouds or sheets of interstellar dust in its vicinity and along the line of sight to us. The arrival of the scattered light is delayed from the arrival of the direct signal, resulting in apparent rings that expand in time. Some of the more spectacular examples are illustrated here.

Light Echoes from V838 Mon in 2002 from the Hubble Space Telescope, and animation

Light Echoes from Supernova 1987A from the Anglo-Autralian Telescope