Peck, William G. (William Guy), 1820-1892 · New York, Chicago, A. S. Barnes & company · leaf 167
me-times they are seen in vast numbers, and then again not aspot is to be seen ; an occasional spot may last for many 162 ASTEOKOMY. weeks, but such persistency is exceptional; as a rule, thespots only continue for a few days, and not infrequentlythey close up and disappear in the course of a few… … Fig. 72 Sun Spots. Drawn by Trouvelot. A fully developed sun-spot, like the right-hand one inFig. 72, consists of a dark central portion called the nu-cleus, surrounded by a lighter border called the penum-bra. The nucleus is separated from the penumbra, and thepenumbra from the photosphere, by…
Astronomy
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