Dumbell planetary nebula (M27). This object comprises shells of gas cast off by a Sun-like star towards the end of its life. The ejection of the star's outer layers exposes its hot core, ultraviolet radiation from which ionises the gases in the shells, causing them to glow. Planetary nebulae are short lived in astronomical terms, lasting around 10,000 years. After this, the central star is too cool to ionise the increasingly distant and diffuse gas shells, and the nebula fades from view. The nebula lies 1360 light years from Earth in the constellation Vulpecula. Different colours represent different ionised gases; sulphur is red, hydrogen is green and oxygen is blue.