planetary nebula

noun

, Astronomy.

1. an expanding shell of thin ionized gas that is ejected from and surrounds a hot, dying star of about the same mass as the sun; the gas absorbs ultraviolet radiation from the central star and reemits it as visible light by the process of fluorescence.

planetary nebula

noun

1. an expanding shell of gas surrounding a dying star, formed from matter ejected from the star's outer layers; the gas is ionized by the remaining hot stellar core, emitting light in the process

planetary nebula

/ plăn′ĭ-tĕr′ē /

1. A nebula consisting of a rapidly expanding shell of glowing gas, mostly hydrogen, ejected from a red giant upon its collapse into a white dwarf. Ultraviolet radiation from the hot, luminous white dwarf ionizes the expanding gas and causes it to glow. The nebula disappears once the cooling dwarf can no longer ionize it, and its material eventually returns to the interstellar medium.
2. See more at white dwarf

Word History and Origins

Origin of planetary nebula¹

First recorded in 1850–55; so named for its resemblance to the planets Uranus and Neptune

Word History and Origins

Origin of planetary nebula¹

C18: named from its (occasional) resemblance to a planetary disc

Example Sentences

Multiple theories were proposed to explain the origin of ORCs, including planetary nebulae and black hole mergers, but radio data alone could not discriminate between the theories.

From Science Daily

Astronomers think that the structure is unique to ageing red-giant stars that will soon end to become planetary nebulae.

From Space Scoop

"We always knew planetary nebulae were pretty. What we see now is spectacular."

From BBC

The colorful cloud in the image—somewhat misleadingly called a planetary nebula—is only a few thousand years old.

From Scientific American

Protostars are very young stars that are still growing in mass via its parent molecular cloud; such objects may have yet to absorb or expel the remaining gas and dust in their planetary nebulae.

From Salon