umbra

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umbrasearch for term: The darkest part of a shadow. In astronomy, umbra can refer to the darkest areas of phenomena such as eclipses and sunspots. For example, the umbra is the darkest region of shadow cast by the Sun or Moon during an eclipse. If an observer stood within the Moon's umbra during a solar eclipse, the Sun would "disappear" behind the Moon. Likewise, the Moon disappears from view when it passes through Earth's umbra during a total lunar eclipse. The umbra is also the darkest region of a sunspot, where the sunspot temperatures are lowest.