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Definition of penumbra - 8 dictionary results

pe⋅num⋅bra

  [pi-nuhm-bruh]
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–noun, plural -brae  [-bree] , -bras.
1. Astronomy.
a. 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. Compare umbra (def. 3a).
b. the grayish marginal portion of a sunspot. Compare umbra (def. 3b).
2. a shadowy, indefinite, or marginal area.
Origin:
1660–70; < NL, equiv. to L paen- pen- + umbra shade

Related forms:
pe⋅num⋅bral, pe⋅num⋅brous, adjective
Dictionary.com Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2009.
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pe·num·bra   (pĭ-nŭm'brə)   
n.   pl. pe·num·brae (-brē) or pe·num·bras
  1. A partial shadow, as in an eclipse, between regions of complete shadow and complete illumination. See Synonyms at shade.
  2. The grayish outer part of a sunspot.
  3. An area in which something exists to a lesser or uncertain degree: "The First Amendment has a penumbra where privacy is protected from governmental intrusion" (Joseph A. Califano, Jr.)
  4. An outlying surrounding region; a periphery: "Downtown Chicago and its penumbra also stand rejuvenated" (John McCormick).

[New Latin pēnumbra : Latin paene, almost + Latin umbra, shadow.]
pe·num'bral, pe·num'brous adj.
The American Heritage® Dictionary of the English Language, Fourth Edition
Copyright © 2009 by Houghton Mifflin Company.
Published by Houghton Mifflin Company. All rights reserved.
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Penumbra

Pe*num"bra\, n. [NL., fr. L. paene almost + umbra shade.]

1. An incomplete or partial shadow.

2. (Astron.) The shadow cast, in an eclipse, where the light is partly, but not wholly, cut off by the intervening body; the space of partial illumination between the umbra, or perfect shadow, on all sides, and the full light. --Sir I. Newton.

Note: The faint shade surrounding the dark central portion of a solar spot is also called the penumbra, and sometimes umbra.

3. (Paint.) The part of a picture where the shade imperceptibly blends with the light.
Webster's Revised Unabridged Dictionary, © 1996, 1998 MICRA, Inc.
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Language Translation for : penumbra
Spanish: crepúsculo,
German: die Abenddämmerung,
Japanese: たそがれ
More Translations »

penumbra 
1666, from Mod.L. penumbra "partial shadow outside the complete shadow of an eclipse," coined 1604 by Kepler from L. pæne "almost" + umbra "shadow."
Online Etymology Dictionary, © 2001 Douglas Harper
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Main Entry: pe·num·bra
Pronunciation: pi-'n&m-br&
Function: noun
Inflected Form: plural -bras
1 : an area within which distinction or resolution is difficult or uncertain 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 penumbra where privacy is protected from governmental intrusion —Griswold v. Connecticut, 381 U.S. 479 (1965)> —see also Griswold v. Connecticut in the IMPORTANT CASES section —pe·num·bral /-br&l/ adjective
Merriam-Webster's Dictionary of Law, © 1996 Merriam-Webster, Inc.
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Main Entry: pe·num·bra
Pronunciation: p&-'n&m-br&
Function: noun
Inflected Form: plural pe·num·brae /-(")brE, -"brI/ or pe·num·bras
: a blurred area in a radiograph at the edge of an anatomical structure —pe·num·bral /-br&l/ adjective
Merriam-Webster's Medical Dictionary, © 2002 Merriam-Webster, Inc.
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penumbra   (pĭ-nŭm'brə)  Pronunciation Key 
Plural penumbras or penumbrae (pĭ-nŭm'brē)
  1. 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. See Note at eclipse.
  2. The grayish outer part of a sunspot. Compare umbra.

The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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penumbra

(from Latin paene, "almost"; umbra, "shadow"), in astronomy, the outer part of a conical shadow, cast by a celestial body, where the light from the Sun is partially blocked-as compared to the umbra (q.v.), the shadow's darkest, central part, where the light is totally excluded. The definition of the term may be extended to include the partial shadow of any large source of light or electromagnetic radiation. An observer in the penumbra sees the Sun (or other light source) partially obscured. The term also is used for the outer portion of a sunspot.

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Encyclopedia Britannica, 2008. Encyclopedia Britannica Online.
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