Moulton, Forest Ray, 1872-1952 · New York, The Macmillan company · leaf 429
29 columns were tipped over so as to make their sides visible.The umbra and penumbra do not gradually merge into eachother, and likewise the penumbra and surrounding photo-sphere have a fairly definite line of separation. The umbra of a sun spot may be anywhere from 500 to50,000 miles across; the… … Fig. 144. — Great sun spot of July 17, 1905. Photographed by Fox with the40-inch telescope of the Yerkes Observatory. have records of observations of sun spots made centuriesbefore their discovery by Galileo in 1610. The umbra of a sun spot is dark only in comparison withthe glowing photosphere…
Astronomy
Internet Archive · Cornell University Library · Public Domain Mark 1.0. Free to use for anything.
