Field guide · Deep sky
Planetary nebulaPlanetary nebula
The glowing shell a Sun-like star puffs off as it dies — nothing to do with planets. Herschel named them: in his telescope they looked like small green discs.
- Made by
- A Sun-like star at the end of its life
- Lasts
- About 10,000–50,000 years
- Leaves behind
- A white dwarf
- Best seen with
- A telescope at medium power
When a star like the Sun runs out of fuel, it swells into a red giant, then gently sheds its outer layers. What is left behind is its exposed core, a white dwarf hotter than any normal star, and its ultraviolet light makes the expanding shell glow.
The glow lasts only some tens of thousands of years before the shell thins into space — an eye-blink for a star — which is why there are only a few thousand in the whole galaxy. They come in rings, hourglasses and butterflies, shaped by the dying star’s spin and by companions.
The name is a 250-year-old mistake: to William Herschel in the 1780s, these small round discs looked like the planet Uranus he had just discovered. The name stuck. This is the Sun’s own future, about five billion years from now.
See it in the sky
Each one opens the sky map pointed at it, for tonight, from where you are.
- Planetary nebula Ring Nebula The Ring in Lyra: a smoke ring the size of a small planet in the eyepiece.
- Planetary nebula Dumbbell Nebula The Dumbbell, bright enough for binoculars.
- Planetary nebula Owl Nebula The Owl, two dark eyes in a pale face.
- Planetary nebula Ghost of Jupiter Nebula The Ghost of Jupiter, the same size and colour as the planet.