penumbra
Americannoun
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Astronomy.
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the partial or imperfect shadow outside the complete shadow of an opaque body, as a planet, where the light from the source of illumination is only partly cut off.
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the grayish marginal portion of a sunspot.
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a shadowy, indefinite, or marginal area.
a penumbra of secrecy.
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U.S. Law. a right or set of rights implicit but not expressed in the U.S. Constitution or Bill of Rights.
The principle of the penumbra protects against an imperfect, or incomplete, enumeration of rights.
noun
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a fringe region of half shadow resulting from the partial obstruction of light by an opaque object
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astronomy the lighter and outer region of a sunspot
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painting the point or area in which light and shade blend
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A partial shadow between regions of full shadow (the umbra) and full illumination, especially as cast by Earth, the Moon, or another body during an eclipse. During a partial lunar eclipse, a portion of the Moon's disk remains within the penumbra of Earth's shadow while the rest is darkened by the umbra.
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See Note at eclipse
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The grayish outer part of a sunspot.
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Compare umbra
Other Word Forms
Derived Forms
Inflected Forms
Nouns
Etymology
Origin of penumbra
First recorded in 1660–65; from New Latin penumbra (coined by Johannes Kepler in 1604), equivalent to Latin paen- prefix meaning “almost” + umbra “shade”; see pen-, umbra
Explanation
When you measure your shadow to calculate the angle of the sun in the sky, be sure to measure to the edges of your shadow, to the penumbra, the part of a shadow that is not as dark as the center. You're likely to come across penumbra most often in astronomy, as with an eclipse, where shadow is a defining feature. In a lunar eclipse, the edge of the earth's shadow — the part that isn't fully dark — is its penumbra. Sun spots also have a penumbra, the outer edge that's not quite as dark as the center. The word comes from the Latin root umbra, which means "shadow." The pen part means "almost," so a penumbra is "almost shadow."
Vocabulary lists containing penumbra
Eclipse Vocabulary
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Space Science (Astronomy) - High School
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Roe v. Wade (1973)
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Example Sentences
Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.
See Examples For:
The lighter one, called the penumbra, will not have too much effect but the umbra, the inner and darker shadow, will darken the Moon.
From BBC ● Sep. 17, 2024
But the Earth also casts a wider, and lighter, shadow, called the penumbra, which extends away from the planet at an angle.
From Slate ● Apr. 5, 2024
Eastern time on Monday, the moon will start to pass through only the outermost part of Earth’s shadow, known as the penumbra.
From New York Times ● Mar. 24, 2024
His non-adult fiction occupies a penumbra between “not really classics” and “better than most of the crap pushed at kids.”
From Los Angeles Times ● Feb. 22, 2023
The late afternoon sun was behind his back, so that he glowed at the edges — shadow, penumbra.
From "Typical American" by Gish Jen
When the ascending currents are powerful, they create those appearances which astronomers designate the nuclei, the penumbrae, the faculae.
From The Story of the Herschels by Anonymous
Her steps became feebler, and she strained her eyes to look afar upon the naked road, now indistinct amid the penumbrae of night.
From Far from the Madding Crowd by Hardy, Thomas
From the top of the terrace he gazed upon this vague form standing up like a phantom in the penumbrae of the evening.
From Salammbo by Flaubert, Gustave
On a December day in the foothills near Seattle, walking into the sun southward and nearly blinded, all you can see are penumbras of emerald-green moss along the vertical edges of the trunks.
From Seattle Times ● Nov. 18, 2022
Rigging raises a sheet, in front of and behind which the dancers play with shadows, misshapen ones with extra auras and penumbras.
From New York Times ● Sep. 11, 2022
Connecticut, that “specific guarantees in the Bill of Rights have penumbras, formed by emanations from those guarantees that . . . create zones of privacy.”
From Washington Post ● Jun. 8, 2018
He wrote, mystically, that “specific guarantees in the Bill of Rights have penumbras, formed by emanations from those guarantees that help give them life and substance.”
From The New Yorker ● May 18, 2015
The deputy pivoted in the direction of the doorway and shouted at a featureless face broken up in equidistant penumbras by four bars, “Who’s there?”
From "The Great Santini" by Pat Conroy
Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023
Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.
