penumbra

noun

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pen·um·bra | \ pə-ˈnəm-brə

plural penumbrae\ pə-ˈnəm-(ˌ)brē

, -ˌbrī \ or penumbras

Definition of penumbra

1a : a space of partial illumination (as in an eclipse) between the perfect shadow on all sides and the full light

b : a shaded region surrounding the dark central portion of a sunspot

2 : a surrounding or adjoining region in which something exists in a lesser degree : fringe the seventeenth century lay in the penumbra of the middle ages— Edward Eggleston

3 : a body of rights held to be guaranteed by implication in a civil constitution the penumbra of the Bill of Rights

4 : something that covers, surrounds, or obscures : shroud a penumbra of secrecy a penumbra of somber dignity has descended over his reputation— James Atlas

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Synonyms for penumbra

Synonyms

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Every solar eclipse casts an umbra, the darker central area in which almost no light reaches the earth, and a penumbra, the area of partial shadow where part of the sun is still visible. Penumbra can thus be used to describe any "gray area" where things aren't all black and white. For example, the right to privacy falls under the penumbra of the U.S. Constitution; though it isn't specifically guaranteed there, the Supreme Court has held that it is implied, and thus that the government may not intrude into certain areas of a citizen's private life. Because its existence is still shadowy, however, the Court is still determining how much of an individual's life is protected by the right to privacy.

Examples of penumbra in a Sentence

the lunar eclipse began with a subtle darkening of the lunar surface as it passed within the Earth's penumbra a penumbra of despair fell over the doomed city

Recent Examples on the Web Partial eclipses happen when the moon is partly in the umbra or entirely in the penumbra with only some sunlight blocked. — Miriam Fauzia, USA TODAY, 26 May 2021 Juliet Williams, a professor of gender studies at UCLA, says Spears' speech can be understood as a penumbra of the #MeToo movement. — Alia E. Dastagir, USA TODAY, 25 June 2021 The entire event then goes into reverse, with the Moon exiting the umbra, then the penumbra. — Jamie Carter, Forbes, 12 May 2021 The action is played out on the golden horizon between reality and legend, the beguiling penumbra where fable and fact coexist. — Moira Hodgson, WSJ, 28 May 2021 Earth always casts two shadows in space opposite the Sun; one fuzzy outer shadow (its penumbra) and one dark inner shadow (its umbra). — Jamie Carter, Forbes, 26 May 2021 The event begins when the full Moon enters the Earth’s outer shadows—its penumbra (a penumbral lunar eclipse). — Jamie Carter, Forbes, 12 May 2021 At that moment, the penumbra will cover 76.5 percent of the lunar disk. — Joe Rao, Scientific American, 17 Oct. 2013 For nearly four hours on Friday, at least some part of the southern portion of the moon will be within Earth's pale penumbra, our planet's faint outer shadow. — Joe Rao, Scientific American, 17 Oct. 2013

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'penumbra.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

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Last Updated

27 Aug 2021

Cite this Entry

“Penumbra.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/penumbra. Accessed 30 Aug. 2021.

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More Definitions for penumbra

penumbra

noun

pe·num·bra | \ pə-ˈnəm-brə

plural penumbrae\ -(ˌ)brē

, -ˌbrī

\ or penumbras

Medical Definition of penumbra

: a blurred area in a radiograph at the edge of an anatomical structure

penumbra

noun

pe·num·bra | \ pi-ˈnəm-brə

plural penumbras

Legal Definition of penumbra

1 : an area within which distinction or resolution is difficult or uncertain the public-private penumbra

2 : an extension of protection, reach, application, or consideration especially : a body of rights held to be guaranteed by implication from other rights explicitly enumerated in the U.S. Constitution the First Amendment has a penumbra where privacy is protected from governmental intrusion — Griswold v. Connecticut, 381 U.S. 479 (1965) — see also Griswold v. Connecticut