A supernova is reborn

A little over 24 years ago, light from the closest supernova in four centuries reached Earth. It was the first such supernova seen in 1987, so it was officially dubbed Supernova 1987A, or SN87A for short. It was full of surprises: the star that blew up (Sanduleak -69 202) was the first blue supergiant ever seen to explode -- most such supernovae progenitors are red supergiants. The intense ultraviolet flash from the explosion lit up a gigantic pre-existing hourglass-shaped shell of gas surrounding the star; over five light years long, nothing quite like it had ever been seen before. The hourglass had a thick ring around its middle, which to this day is still something of a mystery.