penumbra

American  

[pi-nuhm-bruh] / pɪˈnʌm brə /

noun

plural

penumbrae, penumbras

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.

   2. the grayish marginal portion of a sunspot.

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 British  

/ 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 Scientific  

/ pĭ-nŭm′brə /

plural

penumbras

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

---

Other Word Forms

• penumbral adjective
• penumbrous adjective

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”; pen-, umbra

Example Sentences

A lunar eclipse takes place when the Moon passes through the outer region of Earth's shadow, called the penumbra.

From BBC

A lunar eclipse happens when the Moon passes through the outer region of the Earth's shadow called the penumbra.

From BBC

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

Related Words

• dark
• gloom
• obscurity
• shade