penumbra

[ pi-nuhm-bruh ]

noun

, plural pe·num·brae [pi-, nuhm, -bree], pe·num·bras.

1. Astronomy.
   1. 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 ).
   2. the grayish marginal portion of a sunspot. Compare umbra ( def 3b ).
2. a shadowy, indefinite, or marginal area:

   a penumbra of secrecy.

3. 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.

penumbra

/ pɪˈnʌmbrə /

noun

1. a fringe region of half shadow resulting from the partial obstruction of light by an opaque object
2. astronomy the lighter and outer region of a sunspot
3. painting the point or area in which light and shade blend

penumbra

/ pĭ-nŭm′brə /

, Plural penumbras 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.
2. See Note at eclipse
3. The grayish outer part of a sunspot.
4. Compare umbra

Derived Forms

• peˈnumbral, adjective

Other Words From

• pe·num·bral pe·num·brous adjective

Word History and Origins

Origin of penumbra¹

First recorded in 1660–65; from New Latin penumbra (coined by Johannes Kepler in 1604), equivalent to Latin paen- prefix meaning “almost” + umbra “shade”; pen-, umbra

Word History and Origins

Origin of penumbra¹

C17: via New Latin from Latin paene almost + umbra shadow

Example Sentences

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

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

The penumbra of Broadway stardust she radiated accumulated over decades.

From Los Angeles Times

While lit with the penumbra of a spotlight aimed elsewhere, he coolly mimed the smoking of a cigarette with a kazoo.

From New York Times

Maybe it was a fog, or a ghost, or the emanations of the penumbras that come out of the Constitution and offer us guidance.

From Washington Post

Related Words

• dark
• gloom
• obscurity
• shade