Planetary nebula NGC 2818. Hubble Space Telescope (HST) image of the expanding cloud of gas and dust that forms the planetary nebula NGC 2818. A planetary nebula is the outer layers of a star that were ejected after it ran out of fuel to sustain the nuclear reactions in its core. The colours indicate three chemical elements glowing as the cloud impacts with the surrounding interstellar medium: nitrogen (red), hydrogen (green) and oxygen (blue). NGC 2818 is located in the constellation of Pyxis and is around 10,400 light years from Earth. The area seen here is around 6.5 light years across. This image was obtained in 2008, using HST's Wide Field Planetary Camera 2 (WFPC2).