planetary nebula

American  

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.

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planetary nebula British  

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

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planetary nebula Scientific  

/ 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

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Etymology

Origin of planetary nebula

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

Example Sentences

The Dumbbell Nebula, also known as Messier 27, holds a special place in astronomy history as the first planetary nebula ever discovered.

From Science Daily • Jun. 3, 2026

Officially dubbed NGC 3132, a planetary nebula is created when a dying star expels large amounts of mass over a period of successive waves, such as those we see in these pictures.

From Salon • Dec. 26, 2022

This type of structure is called a "planetary nebula", but it actually has nothing to do with planets.

From BBC • Jul. 12, 2022

The Southern Ring, or “Eight-Burst” nebula, is a planetary nebula – an expanding cloud of gas, surrounding a dying star.

From The Verge • Jul. 8, 2022

Every planetary nebula is a token of a star in extremis.

From "Cosmos" by Carl Sagan