This is fun. Watch the supernova remnant Cassiopeia A expand and brighten over a period of 60 years.
This video was made from a series of photographic plates taken between 1951 and 1989 at the Palomar Observatory in California, plus ground-based images taken in 1996 and 1999 by the MDM Observatory, and Hubble observations from 2004 and 2011.
Follow
@kellylepo Fun indeed. You can see the speed of light.
@shuttersparks The entire remnant is about 19 light years across, so light can cross the remnant more than once in the 60 years covered by the video.
What we are seeing is the inward-moving "reverse shock" heating up and then destroying small clumps of gas. The shock is moving at about 5000 kilometers per second. Still very fast, but not quite the speed of light.