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The Cat's Eye Nebula or NGC 6543, is a relatively bright planetary nebula in the northern constellation of Draco, which was discovered by William Herschel on February 15, 1786. It was notably the first planetary nebula whose spectrum was investigated by the English amateur astronomer William Huggins, demonstrating that planetary nebulae were gaseous and not stellar in nature. Structurally, the object has had high-resolution images by the Hubble Space Telescope revealing knots, jets, bubbles and complex arcs, being illuminated by the central hot planetary nebula nucleus or PNN. It is a well-studied object that has been observed from radio to X-ray wavelengths. ==General information== NGC 6543 is a high northern declination deep-sky object and is near the apparent position of the North Ecliptic Pole. It has the combined magnitude of 8.1, with high surface brightness. Its small bright inner nebula subtends an average of 16.1 arcsec, with the outer prominent condensations about 25 arcsec. Deep images reveal an extended halo about 300 arcsec or 5 arcmin across,〔 that was once ejected by the central progenitor star during its red giant phase. Observations show the bright nebulosity has temperatures between and , whose densities average of about particles per cubic centimetre. Its outer halo has the higher temperature around , but is of much lower density. Velocity of the fast stellar wind is about , where spectroscopic analysis shows the current rate of mass loss averages solar masses per year, equivalent to twenty trillion tons per second (20 Eg/s).〔 Surface temperature for the central star is about , being times as luminous as the sun. Stellar classification is O7 + ()–type star〔 Calculations suggest the central star is over one solar mass, from a theoretical initial 5 solar masses. Radius is about 0.65 times the Sun or . The Cat's Eye nebula, given in some sources, lies about three thousand light-years from Earth. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Cat's Eye Nebula」の詳細全文を読む スポンサード リンク
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