varying values for elemental abundances. This is often because spectrographs attached to telescopes do not collect all the light from objects being observed, instead gathering light from a slit or small aperture. Therefore, different observations may sample different parts of the nebula. However, results for NGC 6543 broadly agree that, relative to hydrogen, the helium abundance is about 0.12, carbon and nitrogen abundances are both about , and the oxygen abundance is about . These are fairly typical abundances for planetary nebulae, with the carbon, nitrogen and oxygen abundances all larger than the values found for the sun, due to the effects of nucleosynthesis enriching the star's atmosphere in heavy elements before it is ejected as a planetary nebula. Deep spectroscopic analysis of NGC 6543 may indicate that the nebula contains a small amount of material which is highly enriched in heavy elements; this is discussed below. Kinematics and morphology The Cat's Eye Nebula is structurally a very complex nebula, and the mechanism or mechanisms that have given rise to its complicated morphology are not well understood. The central bright part of the nebula consists of the inner elongated bubble (inner ellipse) filled with hot gas. It, in turn, is nested into a pair of larger spherical bubbles conjoined together along their waist. The waist is observed as the second larger ellipse lying perpendicular to the bubble with hot gas. The structure of the bright portion of the nebula is primarily caused by the interaction of a fast stellar wind being emitted by the central PNN with the visible material ejected during the formation of the nebula. This interaction causes the emission of X-rays discussed above. The stellar wind, blowing with the velocity as high as , has 'hollowed out' the inner bubble of the nebula, and appears to have burst the bubble at both ends. It is also suspected that the central WR:+O7 spectral class PNN star, HD 164963 / BD +66 1066 / PPM 20679 of the nebula may be generated by a binary star. The existence of an accretion disk caused by mass transfer between the two components of the system may give rise to polar jets, which would interact with previously ejected material. Over time, the direction of the polar jets would vary due to precession. Outside the bright inner portion of the nebula, there are a series of concentric rings, thought to have been ejected