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

While about half its mass will flood out, the rest will crush together at the very center of the planetary nebula.

From Popular-Science

A star has actually, under our eyes, become a planetary nebula, and the cycle of which he gave the first terms is complete.

From Project Gutenberg

Its visual appearance in the great telescope was now also that of a planetary nebula.

From Project Gutenberg

For a glance at a planetary nebula we may turn with the five-inch to No. 4234.

From Project Gutenberg