A 10-year-old girl in Canada has become the youngest person to discover a supernova – an exploding star which can briefly outshine a whole galaxy. Kathryn Gray was studying images taken at an amateur observatory which had been sent to her father. She spotted the magnitude 17 supernova on Sunday. Supernovas – which are rare events – are stellar explosions that mark the violent deaths of stars several times bigger than the Sun. The supernova was discovered in the galaxy UGC 3378, about 240 million light years away, in the constellation of Camelopardalis. The new supernova is called Supernova 2010lt. The last supernova in our galaxy occurred several hundred years ago.