Cassiopeia A (Cas A) is a supernova remnant located about 11 000 light-years from Earth in the constellation Cassiopeia. It spans approximately 10 light-years.
On the left is the object as seen by the NASA/ESA/CSA James Webb Space Telescope. On the right is the object as seen by the NASA/ESA Hubble Space Telescope in 2004. The nearly two decades of elapsed time between the two images has made the expansion of the nebula discernible between the visible (Hubble) and infrared (Webb) images.
NASA, ESA, CSA, D. Milisavljevic (Purdue University), T. Temim (Princeton University), I. De Looze (UGent), J. DePasquale (STScI), the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration. Acknowledgement: R. A. Fesen (Dartmouth College, USA) and J. Long (ESA/Hubble)