From his private observatory in South London, William Huggins was examining one of the most intriguing objects in the night sky — an elongated blob that resembles a cat’s eye.
Huggins was using a new instrument, called a spectroscope. When aimed at a star, it produces a rainbow of colors with some dark, narrow gaps — the “fingerprints” of elements in the star’s outer layers. But when Huggins aimed it at the cat’s eye 150 years ago today, there was no rainbow at all. Instead, he saw one thin blue line and two even thinner green ones.
Huggins realized that this object wasn’t a star at all, but a nebula — a cloud of glowing gas. The blue line came from hydrogen, but Huggins had no idea what produced the green ones. He called this mysterious new element “nebulium.”
It took a while for astronomers to work out the nature of the Cat’s Eye Nebula: It’s the last gasp of a dying star. The star’s outer layers are streaming into space at thousands of miles per hour, forming colorful bubbles.