The magnificent planetary nebula NGC 6543 in Draco is also known as the Cat's Eye nebula. It has a bright, bluish disk and a faint central star visible in large telescopes.
This prominent northern object was missed by Charles Messier and discovered by William Herschel, on February 15, 1786. The Cat Eye Nebula was the first planetary to be investigated spectroscopically, by the English amatuer astronomer William Huggins in 1864 - in the same volume where John Herschel published his General Catalog (GC) of deep sky objects.
Observation
NGC 6543 is situated midway between δ and ζ Dra, almost exactly in the direction of the North Ecliptic Pole. This means a vector perpendicular to the Earth's orbital plane points very close to this nebula, and that diagrams of planetary orbits represent a view of them as seen from this planetary.
This 8.1-magnitude planetary nebula is one of the brightest of its type. A 4" telescope will show a foggy blue-green disk about 0.3' (18 arcseconds) across, embedded in a fainter halo 5.8' across. Its resemblance to a cat’s eye is due to a series of gas loops that have been ejected by the central star over the past 1,000 years or so. It is one of the most complex nebulae known, but more powerful instruments are needed to reveal its internal structure.
Properties and Evolution
NGC 6543 is a young planetary nebula, about 3300 light years away. The great complexity of the Cat's Eye's structure - with its concentric gas shells, jets of high-speed gas, and unusual shock-induced knots of gas - suggests that the central star may be a binary system. If the companion were pulling in material from a neighboring star, jets escaping along the companion’s rotation axis could be produced. The fact that the twin jets are now pointing in different directions suggests that they are wobbling, or precessing, and turning on and off periodically.
Further astonishing detail of the Cat's Eye emerged in 2004, following new Hubble Space Telescope images. The images revealed a pattern of at least 11 concentric shells, around the inner portion of the nebula. These suggest that the star ejected its mass in a series of pulses at 1,500-year intervals. These convulsions created dust shells, each containing as much mass as all the planets in our Solar System combined.
About 1,000 years ago the pattern of mass loss suddenly changed, and the Cat's Eye Nebula started forming inside the dusty shells. It has been expanding ever since, as discernible in comparing Hubble images taken in 1994, 1997, 2000, and 2002. The puzzle is what caused this dramatic change.
Despite intensive study, the Cat's Eye Nebula still holds many mysteries. The study of planetary nebulae like NGC 6543 is one of the few ways to recover information about these last few thousand years in the life of a Sun-like star.