Published online by Cambridge University Press: 14 August 2015
The planetary nebula NGC 6543 has been described (Curtis, 1918) as “quite irregular, of helical form”. Its high surface brightness and its dimensions (16′′ × 22′′ of arc) make it an ideal object for observation with the multislit technique used by Wilson (1950) to study other planetaries. In fact, had NGC 6543 been accessible to the 100-inch Mount Wilson Coudé, undoubtedly it would have been included in Wilson's survey. The interest in NGC 6543 arises from the fact that no information is available regarding the motions in a planetary nebula with some sort of helical appearance. The obvious question that arises in this respect is whether the nebular material is actually arranged in space on an open helix, rather than in a flat spiral. The related problems of its lifetime and stability also may be elucidated by studying in detail the internal motions.