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A large, circular emission nebula in the southern constellations Vela and Puppis,
discovered by an Australian astronomer, Colin Gum. The nebula is 30° across,
which is equivalent to a diameter of 800 light years at its distance of 1,300 light
years. It is thought to be the result of ionization of the interstellar medium
caused by a supernova that exploded perhaps a million years ago. This would mean
that there is no longer a source of energy, and the nebula is now gradually
fading as ionized hydrogen recombines and ceases to be luminous.
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