- A ring-shaped nebula formed by an expanding shell of gas round an ageing star.More example sentences
- Astronomers call such an object a planetary nebula, because its round shape resembles that of a planet when viewed with a small telescope.
- The Boomerang Nebula is a young planetary nebula and the coldest object found in the Universe so far.
- Until recently, it was thought that shells around planetary nebulae were a rare phenomenon.
More definitions of planetary nebulaDefinition of planetary nebula in:
- The US English dictionary