Helix Nebula. Hubble Space Telescope image of part of the Helix planetary nebula (NGC 7293). This comprises shells of gas cast off a Sun-like star near the end of its life. The colours are due to gases in the shells being ionised by radiation from the star (not seen) that ejected them. The blue colour comes from oxygen and the red from hydrogen and nitrogen. The spoke-like structures, which all point to the central star, are thought to have formed by the action of the star's wind on the ejected gases. This is one of the nearest planetary nebulae to Earth, lying 650 light years away in the constellation Aquarius.