penumbra
noun
Edward EgglestonJames Atlas
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Every solar eclipse casts an umbra, the darker central area in which almost no light reaches the earth, and a penumbra, the area of partial shadow where part of the sun is still visible. Penumbra can thus be used to describe any "gray area" where things aren't all black and white. For example, the right to privacy falls under the penumbra of the U.S. Constitution; though it isn't specifically guaranteed there, the Supreme Court has held that it is implied, and thus that the government may not intrude into certain areas of a citizen's private life. Because its existence is still shadowy, however, the Court is still determining how much of an individual's life is protected by the right to privacy.
Examples of penumbra in a Sentence
Ashley Strickland, CNN, 13 Mar. 2025
What Will Happen During The Total Lunar Eclipse The five stages of the total lunar eclipse are:
1st penumbral phase (72 minutes): the moon drifts into Earth’s outer shadow in space, its penumbra.
—Jamie Carter, Forbes, 12 Mar. 2025
The entire eclipse process is projected to end by 6 a.m. as the moon slowly exits the Earth's penumbra, NASA explains.
—Eric Lagatta, USA TODAY, 19 Feb. 2025
The umbra is much darker than the penumbra and fairly sharp-edged.
—Joe Rao, Space.com, 9 Mar. 2025
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Cite this Entry
“Penumbra.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/penumbra. Accessed 28 Mar. 2025.
Copy CitationKids Definition
penumbra
noun
Medical Definition
penumbra
noun
Legal Definition
penumbra
noun
Griswold v. Connecticut, 381 U.S. 479 (1965) 
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