Two-Star Collision Yields Three-Ring Nebula. Challis Supernova 1987 occurred in the Large Magellanic Cloud, a galaxy only light years from Earth. The outburst was visible to the naked eye, and is the brightest known supernova in almost 400 years.
Cassiopeia A, an exploded star light-years away. The green ring surrounding the supernova is from the initial shock wave generated by the explosion; it measures 10 light years in diameter. - by the Chandra X-Ray Observatory - Credit: NASA