What does umbra mean?
Umbra is the technical term for the completely shaded central region of a shadow. It is especially important in astronomy, where it names the region in which the Sun is entirely blocked by another celestial body. During a total solar eclipse, totality occurs for observers positioned within the Moon’s umbra. The surrounding area, where the Sun is only partly covered, is called the penumbra. Although umbra can also mean a shadow or shade in formal and literary writing, its modern use is largely specialized. In scientific contexts, the word precisely distinguishes full obscuration from partial shadow. The distinction is useful when describing eclipses and the geometry of shadows cast by opaque objects. Umbra entered English from Latin, where it originally meant “shadow” or “shade,” and it later became established astronomical terminology.
nounThe fully shaded central part of a shadow, especially the region in which the light source is completely obscured, as during an eclipse. More generally, it can mean a shadow or shade.
- The fully shaded central region of a shadow, especially during an eclipse, where the light source is completely obscured.
- A shadow or shade, especially in formal or literary usage.
"The spacecraft entered the umbra of the planet and fell silent as its radio signal was blocked."
"The aircraft passed directly through the umbra of the Moon during the eclipse."
"Deep umbra filled the alcove, concealing the old stonework."
The usual plural is umbras, although umbrae is also used in astronomical writing.
"The two umbras converged across the surface of the distant planet."
During a total solar eclipse, observers experience totality only inside the Moon’s narrow umbra.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does umbra come from?
Umbra was borrowed into English in the early 17th century from Latin umbra, meaning “shadow” or “shade.” Its specialized astronomical sense developed from the same Latin terminology for the central, fully dark part of a shadow. The word also underlies forms such as umbrella, umbrage, umbrous, and umbraculum, all of which relate to shade, covering, or shadow.
How umbra is actually used
The word is specialized and relatively formal, occurring chiefly in astronomy, optics, and literary descriptions of shade rather than in everyday speech.
Easily confused with umbra
Umbra is a region of complete shadow, whereas umber is a brown pigment or a shade of brown.
The umbra is the region where the light source is completely blocked, while the penumbra is the surrounding region where it is only partly blocked.