...One penumbra will sometimes enclose several umbræ whilst the nucleimay be entirely wanting... 
Thomas Orchard 「The Astronomy of Milton's 'Paradise Lost'」
...13, in which the dark centralnucleus appears in sharp contrast with the lighter margin or penumbra...
Robert Stawell Ball 「The Story of the Heavens」
...Wherever the penumbra falls there will be a solareclipse of some kind, and the nearer the place is to the axisof the penumbra, the more nearly total will be the eclipse...
George C. Comstock 「A Text-Book of Astronomy」
...Grover has not only seen theabove-named features, but even a penumbra to the shadow on the ringswith a 2-inch telescope...
Richard A. Proctor 「Half-hours with the Telescope」
...): the penumbra continued uponher disc for an hour afterwards...
George Chambers 「The Story of Eclipses」
...The penumbra attending the earth's shadow is usually supposed to render this observation uncertain to two or three minutes of time, or more than half a degree of longitude...
Matthew Flinders 「A Voyage to Terra Australis」
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