Cassiopeia A is a supernova remnant in the constellation Cassiopeia and the brightest extrasolar radio source in the sky.
The supernova occurred approximately 11,000 light-years away within the Milky Way.
It is believed that first light from the stellar explosion reached Earth approximately 300 years ago but there are no historical records of any sightings of the supernova that created the remnant, probably due to interstellar dust absorbing optical wavelength radiation before it reached Earth
