Jellyfish nebula (IC 443, centre). This is the remnant of a supernova. When a large star dies, gas shells explode outwards and collide with interstellar material. The energy of the collision ionises the gas, causing it to glow. The bright star at right is Eta Geminorum, the bright star at left is Mu Geminorum. The jellyfish nebula lies 5000 light years from Earth in the constellation Gemini. Different colours represent different ionised gases; sulphur is red, hydrogen is green and oxygen is blue.