A new manual of the elements of astronomy, descriptive and mathematical .. (1868)
Kiddle, Henry, 1824-1891 · New York, Ivison, Phinney, Blakeman & co.; Chicago, S.C. Griggs & co. · leaf 110
■> 8OLAB SPOTS. a. Sometimes the nucleus is absent; and sometimes spots are seenwithout any penumbra. The nucleus is not of a uniform blackness,but generally contains an intensely black spot in the centre. Thesespots usually appear in clusters, numbering from two to sixty or sev-enty, or even…
Astronomy
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