Helix planetary nebula. Optical image of the Helix planetary nebula (NGC 7293). This is the nearest planetary nebula to Earth, lying about 450 light years away in the constellation Aquarius. Planetary nebulae are expanding shells of gas cast off by a dying star as it contracts to become a white dwarf. The shells emit light as the gas they contain is ionised by radiation from the star. Their misleading name arose due to their similar appearance to planets through early telescopes. This image was produced by the CFH12K CCD camera on the Canada-France-Hawaii Telescope on Mauna Kea, Hawaii, USA.