Definition of penumbra in English:

penumbra

Syllabification: pe·num·bra
Pronunciation: /peˈnəmbrə
 
/

noun (plural penumbrae /-brē, -brī/ or penumbras)

  • 1The partially shaded outer region of the shadow cast by an opaque object.
    More example sentences
    • In other cases the Moon does not pass through the umbra at all, just going through the penumbra (a region of partial shadow).
    • And we would do well to remember that the penumbra is the lighter, outer region of the shadow, the halo, indeed, of the shadow.
    • The Moon begins to enter the Earth's outer shadow, or penumbra, at 9: 06 P.M.
  • 1.1 Astronomy The shadow cast by the earth or moon over an area experiencing a partial eclipse.
    More example sentences
    • On Friday morning, the moon will enter the penumbra of the Earth's shadow at 3: 05 am, and the moonlight will become dimmer.
    • So, one will observe either a total eclipse by the umbra (which can be well observed), a partial eclipse by the umbra and penumbra, or a total or partial eclipse by the penumbra only.
    • The Moon on April 24th will glide through Earth's penumbra, producing what astronomers call a ‘penumbral lunar eclipse.’
  • 1.2 Astronomy The less dark outer part of a sunspot, surrounding the dark core.
    More example sentences
    • Theorists suspect that the penumbra is key to keeping a sunspot intact.

Derivatives

penumbral

adjective
More example sentences
  • I think it's important that we recognize the existence of this problematic, penumbral group, but that doesn't mean that there aren't people who do take responsibility.
  • Rick would howl, and then rapidly half-wade, half-swim down the penumbral corridor and stumble up onto the next sandbank, laughing.
  • The nearly flat trail was bordered on one side by precipitous slopes, where penumbral snowfields fell into the crater 100 feet below.

Origin

mid 17th century: modern Latin, from Latin paene 'almost' + umbra 'shadow'.

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