Supernova remnant Simeis 147. 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 star is thought to have exploded around 30,000 years ago. Simeis 147 lies 3000 light years away in the constellation Taurus. Different colours represent different ionised gases; sulphur is red, hydrogen is green and oxygen is blue.