The Cat’s Eye Nebula
Posted by Brian Ventrudo
Turn your gaze this week to the far-northern constellation Draco to see a newly dying star dispatching its outer layers as a complex and elegant nebula, a planetary nebula known as the “Cat’s Eye”. Just a thousand years old, the Cat’s Eye displays an amazing amount of complexity, and gives you a glimpse of our own Sun’s distant future…
The Cat’s Eye, cataloged as NGC 6543, is the only planetary nebula in the long constellation Draco which winds between the Big and Little Dippers. The nebula is located about halfway between the stars delta (δ) and zeta (ζ) Draconis. At 30-40x, you’ll just be able to discern the nebula from the surrounding stars. It looks slightly fuzzy, with perhaps a greenish color. More magnification (100x or more) will show you its true nature.
In the 18th and 19th centuries, astronomers thought planetary nebula were patches of unresolved stars. But the English amateur astronomer William Huggins turned a spectroscope to the Cat’s Eye and discovered its light was completely different from any star. He attributed the strange spectrum to an undiscovered element he called “nebulium”. Decades later, spectroscopists determined “nebulium” was really a form of ionized oxygen that exists only in the rarified vacuum of space. This type of oxygen ion is called OIII (“Oh-Three”). You can now get OIII filters to attach to the eyepiece of your telescope to pass the light from this ion and increase the contrast against the background sky of the Cat’s Eye and other nebulae.
While the Cat’s Eye is modest in a backyard scope, it is dazzling in long-exposure photographs. A splendid image from the Hubble Telescope made this nebula famous nearly two decades ago. Here’s an updated image from the HST…
And the most amazing thing about the Cat’s Eye? Nearly all its wispy structure, which is caused by the intermittent gasps of a dying star like our sun, is quite new… less than a thousand years old. So unlike most astronomical events, planetary nebulae like the Cat’s Eye Nebula happen quickly and briefly. Our own star will experience the same quick and final fate in some 5 billion years.