Helix Nebula. Hubble Space Telescope image 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 central star that ejected them. The blue colour comes from oxygen and the red from hydrogen and nitrogen. Despite its ring shape, it is thought that the nebula is actually a cylinder aligned end on to Earth. This is one of the nearest planetary nebulae to Earth, lying 650 light years away in the constellation Aquarius. It is 3 light years in diameter, and appears half a Moon-width wide.