supernova:  When a very large star is at the end of its life cycle and uses up all its fuel it explodes.  The explosion is called a supernova.  The explosion is very violent.  The supernova may shine for days or weeks.  A supernova shines with the brightness of 100 billion other stars put together!  When a star becomes a supernova, it blasts away its outer layers.  The material that the supernova throws into space may form a nebula.