One of the extreme northern sky’s most entertaining deep-sky objects, the Cat’s Eye Nebula in Draco (NGC 6543), is a planetary nebula with a high surface brightness. Discovered by William Herschel in 1786, it was the first planetary whose spectrum was observed, in 1864, by William Huggins. He therefore demonstrated that planetary nebulae are gaseous. Its overall magnitude is 8.1; its small, bright disk measures 20” across; and the outer halo extends to 5.8’. At its distance of 3,300 light-years, this corresponds to a diameter of about 0.4 light-year.
The Cat’s Eye is a young planetary, at perhaps 1,000 years. In part because of this, it shows the multiple stages of a planetary nebula well. The inner, higher-speed gas is slamming into the outer, slower, “belched” halo, creating an ionization front.
The Cat’s Eye has a very complex inner structure and the mechanism behind this is not yet well understood. The nebula’s structural complexity can be seen by visual observers with high magnifications on nights of steady seeing. Large telescopes reveal hints of the multiple “spiral” structure of the inner nebula, so vividly seen in images made with the Hubble Space Telescope.
