Excerpt: ...of the individual spots were large enough to contain the earth if it had been dropped upon them. From Fig. 67 determine in miles the length of the group on August 14th. Fig. 71 shows an enlarged view of these spots as they appeared on August 17th, and in this we find some details not so well shown in the preceding pictures. The larger spots consist of a black part called the nucleus or umbra (Latin, shadow), which is surrounded by an irregular border called the penumbra (partial shadow), which is intermediate in ...
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Excerpt: ...of the individual spots were large enough to contain the earth if it had been dropped upon them. From Fig. 67 determine in miles the length of the group on August 14th. Fig. 71 shows an enlarged view of these spots as they appeared on August 17th, and in this we find some details not so well shown in the preceding pictures. The larger spots consist of a black part called the nucleus or umbra (Latin, shadow), which is surrounded by an irregular border called the penumbra (partial shadow), which is intermediate in brightness between the nucleus and the Pg 193 surrounding parts of the sun. It should not be inferred from the picture that the nucleus is really black or even dark. It shines, in fact, with a brilliancy greater than that of an electric lamp, but the background furnished by the sun's surface is so much brighter that by contrast with it the nucleus and penumbra appear relatively dark. Fig. 71.
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