^Ilya G. Usoskin, Kalevi Mursula, Rainer Arlt, Gennady A. Kovaltsov. A Solar Cycle Lost in 1793-1800: Early Sunspot Observations Resolve the Old Mystery. The Astrophysical Journal Letters. 2009, 700 (2): L154 [2018-04-02]. ISSN 1538-4357. doi:10.1088/0004-637x/700/2/l154(英语).
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