- Derived from the Latin from ‘almost a shadow,’ the term is used in two ways in astronomy. The first applies to eclipses and refers to the area which is partially rather than wholly in shadow. During an eclipse of the Sun there is a narrow area of totality in which the completely eclipsed sun is seen Surrounding this is a much larger area where the Sun is only partly shadowed, where the penumbra reaches the Earth’s surface. In an eclipse of the Moon, two types of darkening of the lunar surface are seen. The central darkest area is in the umbra and the area of lesser darkening around it in the penumbra. The second usage relates to sunspots, where the paler area surrounding the darker centre of the spot is the penumbra.
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