Astron. Nachr. / AN 999, No. 88, 789 – 828 (2011) / DOI please set DOI! Sunspot numbers based on historic records in the 1610s – early telescopic observations by Simon Marius and others R. Neuhauser¨ 1 ? and D.L. Neuhauser¨ 2 1 Astrophysikalisches Institut und Universitats-Sternwarte,¨ FSU Jena, Schillergaßchen¨ 2-3, 07745 Jena, Germany (e-mail:
[email protected]) 2 Schillbachstraße 42, 07743 Jena, Germany Received 2015 Sep 24, accepted 2016 Mar 9 Key words sunspots – Simon Marius – solar activity – Maunder Minimum – history of astronomy Hoyt & Schatten (1998) claim that Simon Marius would have observed the sun from 1617 Jun 7 to 1618 Dec 31 (Gregorian calendar) all days, except three short gaps in 1618, but would never have detected a sunspot – based on a quotation from Marius in Wolf (1857), but mis-interpreted by Hoyt & Schatten. Marius himself specified in early 1619 that for one and a half year ... rather few or more often no spots could be detected ... which was never observed before (Marius 1619). The generic statement by Marius can be interpreted such that the active day fraction was below 0.5 (but not zero) from fall 1617 to spring 1619 and that it was 1 before fall 1617 (since August 1611). Hoyt & Schatten cite Zinner (1952), who referred to Zinner (1942), where observing dates by Marius since 1611 are given, but which were not used by Hoyt & Schatten. We present all relevant texts from Marius where he clearly stated that he observed many spots in different form on and since 1611 Aug 3 (Julian) = Aug 13 (Greg.) (on the first day together with Ahasverus Schmidnerus); 14 spots on 1612 May 30 (Julian) = Jun 9 (Greg.), which is consistent with drawings by Galilei and Jungius for that day, the latter is shown here for the first time; at least one spot on 1611 Oct 3 and/or 11 (Julian), i.e.