umbra


umbra

noun, plural um·bras, um·brae [uhm-bree] /ˈʌm bri/.

  1. shade; shadow.
  2. the invariable or characteristic accompaniment or companion of a person or thing.
  3. Astronomy.
    1. the complete or perfect shadow of an opaque body, as a planet, where the direct light from the source of illumination is completely cut off.Compare penumbra(def 1a).
    2. the dark central portion of a sunspot.Compare penumbra(def 1b).
  4. a phantom or shadowy apparition, as of someone or something not physically present; ghost; spectral image.

noun plural -brae (-briː) or -bras

  1. a region of complete shadow resulting from the total obstruction of light by an opaque object, esp the shadow cast by the moon onto the earth during a solar eclipse
  2. the darker inner region of a sunspot

n.1590s, “phantom, ghost,” a figurative use from Latin umbra “shade, shadow” (see umbrage). Astronomical sense of “shadow cast by the earth or moon during an eclipse” is first recorded 1670s. Meaning “an uninvited guest accompanying an invited one” is from 1690s. Plural umbras umbrae (ŭmbrē)

  1. The darkest part of a shadow, especially the cone-shaped region of full shadow cast by Earth, the Moon, or another body during an eclipse. In a full lunar eclipse, which generally lasts for one or two hours, the entire disk of the Moon is darkened as it passes through the umbra. During this period the Moon takes on a faint reddish glow due to illumination by a small amount of sunlight that is refracted through the Earth’s atmosphere and bent toward the darkened Moon; the reddish tint is caused by the filtering out of blue wavelengths as the sunlight passes through the Earth’s atmosphere, leaving only the longer wavelengths on the red end of the spectrum. See Note at eclipse.
  2. The dark central region of a sunspot. Compare penumbra.

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