umbra

American  

[uhm-bruh] / ˈʌm brə /

noun

plural

umbras, umbrae

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.

   2. the dark central portion of a sunspot.

4. a phantom or shadowy apparition, as of someone or something not physically present; ghost; spectral image.

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umbra British  

/ ˈʌmbrə /

noun

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

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umbra Scientific  

/ ŭm′brə /

plural

umbras

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.

2. See Note at eclipse

3. The dark central region of a sunspot.

4. Compare penumbra

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Other Word Forms

• umbral adjective

Etymology

Origin of umbra

First recorded in 1600–10; from Latin: literally, “shade, shadow”

Explanation

The very darkest part of a shadow is the umbra. It's where the light source is completely blocked by the object in front of it. You'll most often encounter the word umbra in astronomy, along with penumbra and sometimes antumbra. During a lunar eclipse, the very darkest, inner part of the Earth's shadow is the umbra, while the lighter shadow at the edge is the penumbra. The antumbra is the bright ring you can sometimes see around the shadow. Umbra is a Latin word that means "shadow."

Example Sentences

When the moon is within the umbra, the darkest part of Earth’s shadow, it looks red-orange, giving the eclipse the name “blood moon.”

From Los Angeles Times • Mar. 11, 2025

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 • Sep. 17, 2024

And when the moon is fully in the umbra, that’s a total eclipse.

From Slate • Apr. 5, 2024

“Having once stood in the umbra, the Moon’s shadow, during a solar eclipse, we are driven to do so again and again, whenever the Moon moves between the Earth and the Sun.”

From New York Times • Apr. 2, 2024

All were in the umbra of the magnificent hemlock.

From "Frightful's Mountain" by Jean Craighead George

Related Words

• body
• character
• creature
• ghost
• human being
• individual
• man
• person
• spirit
• woman