The "light echo" is interesting. They say the supernova happened 350 years ago; and that "Baby Cas A" is 170 light-years behind Cas A. So the echo "caught up"

The "light echo" is interesting. They say the supernova happened 350 years ago; and that "Baby Cas A" is 170 light-years behind Cas A. So the echo "caught up" with light coming our way about 340 years ago; that is, the echo consists of light that was emitted just 10 years after the explosion. Have I got that right? [Edit] The "echo" isn't really a reflection; it's emission from a gas-cloud heated by the original explosion, as it cools down. So it's not really reflected light from the original event.