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New information on solar activity, 1779-1818, from Sir William Herschel's unpublished notebooks
Hoyt, Douglas V.; Schatten, Kenneth H.
AA(Research and Data Systems Corp., Greenbelt, MD), AB(NASA, Goddard Space Flight Center, Greenbelt, MD)
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 384, Jan. 1, 1992, p. 361-384. (ApJ Homepage)
Publication Date:
Solar Physics
NASA/STI Keywords:
Solar Activity, Sunspots, Astronomical Observatories, Solar Cycles
Bibliographic Code:


Herschel's observations are analyzed in order to determine the level of solar activity for solar cycle 5. It is concluded that solar cycle 5 may have peaked as early as 1801 based upon the average number of groups with a probable secondary maximum in 1804. Depending on the technique adopted, the peak for solar cycle 5 occurred sometime between 1801 and 1804, rather than 1805.2, as commonly assumed. Instead of a solar cycle of 17 yrs, a cycle length of 14 yrs is found. It is also found that the peak yearly mean sunspot number is only about 38 rather than 45, as deduced by Wolf (1855). A technique for making early solar observations homogeneous with modern sunspot observations is proposed.

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