A Reanalysis of the Number of Sunspot Groups Recorded by Pierre Gassendi in the Cycle Before the Maunder Minimum

Abstract

Pierre Gassendi (1592 – 1655) carried out sunspot observations during the 1630s. This period is particularly interesting because it occurred a few years before the Maunder Minimum. Gassendi was the second most active sunspot observer in that decade, surpassed only by Christoph Scheiner. Moreover, the sunspot observations made by Gassendi are of interest because most of them were made in days when no other sunspot observations were available. We have analyzed the sunspot drawings included in his Complete Works (Opera Omnia) and the textual reports with sunspot information after translating them from the original Latin. Thus, we have detected mistakes in previous works that studied these observations, such as incorrect dates and incorrect daily number of groups assigned to Gassendi. In addition, we found some observation days recorded by Gassendi not included in the current sunspot-group-number database. In this work, we provide a new account of the number of groups recorded by Gassendi in addition to the translations of his relevant texts on observed sunspots. Our main objective is to include these new recounts into the current sunspot-group-number database, which is the basis of the group-number index, to have a more accurate knowledge of solar activity of the third solar cycle observed with the aid of the telescope.