before the formation of the planetary nebula, while the star was on the asymptotic giant branch of the Hertzsprung–Russell diagram. These rings are very evenly spaced, suggesting that the mechanism responsible for their formation ejected them at very regular intervals and at very similar speeds. The total mass of the rings is about 0.1 solar masses. The pulsations that formed the rings probably started 15,000 years ago and ceased about years ago, when the formation of the bright central part began (see above). Further, a large faint halo extends to large distances from the star. The halo again predates the formation of the main nebula. The mass of the halo is estimated as 0.26–0.92 solar masses. See also List of largest nebulae Notes References Cited sources External links Cat's Eye Nebula Release at ESA/Hubble Cat's Eye Nebula images at ESA/Hubble Chandra X-Ray Observatory Photo Album: NGC 6543 Astronomy Picture of the Day The Cat's Eye Nebula October 31, 1999 Halo of the Cat's Eye 2010 May 9 The Cat's Eye Nebula 2016 July 3 Hubble Probes the Complex History of a Dying Star—HubbleSite article about the Cat's Eye Nebula. NGC6543 The Cats Eye Nebula Hubble's Color Toolbox: Cat's Eye Nebula—article showing image composite process used to produce an image of the nebula Cat's Eye Nebula at Constellation Guide Cat's Eye Nebula in the Staracle NGC catalog SEDS – NGC 6543 006b Draco (constellation) NGC objects Planetary nebulae Astronomical objects discovered in 1786 Discoveries by William Herschel