Solar activity reconstruction from the Georg Eimmart archive of 1616 – 1720

AbstractHistorical sunspot records provide piece by piece more information on solar variability on a centennial scale. In this work, we analyze sunspot observations from the archives of Georg Christoph Eimmart, which is the second-richest data set of the Maunder minimum after the archives of the Paris observatory. Comparing the dates of the blank solar disk from the database by Hoyt & Schatten (1998) with dates of observations at the Eimmart observatory, we find that spotless days reports originate from astrometric observations. A comparison of the observations by La Hire and Müller of 1719 suggests that the observations by La Hire were for astrometric purposes as well, rather than aimed at sunspot counting.