Sunspot characteristics at the onset of the Maunder Minimum based on the observations of Hevelius

Abstract

An analysis of the sunspot observations made by Hevelius during 1642-1645 is presented. These records are the only systematic sunspot observations just before the Maunder Minimum. We have studied different phenomena meticulously recorded by Hevelius after translating the original Latin texts. We re-evaluate the observations of sunspot groups by Hevelius during this period and obtain an average value 7% greater than that calculated from his observations given in the current group database. Furthermore, the average of the active day fraction obtained in this work from Hevelius' records previous to the Maunder Minimum is significantly greater than the solar activity level obtained from Hevelius' sunspot observations made during the Maunder Minimum (70% vs. 30%). We also present the butterfly diagram obtained from the sunspot positions recorded by Hevelius for the period 1642-1645. It can be seen that no hemispheric asymmetry exists during this interval, in contrast with the Maunder Minimum. Hevelius noted a ~3-month period that appeared to lack sunspots in early 1645 that gave the first hint of the impending Maunder Minimum. Recent studies claim that the Maunder Minimum was not a grand minimum period speculating that astronomers of that time, due to the Aristotelian ideas, did not record all sunspots that they observed, producing thus an underestimation of the solar activity level. However, we show the good quality of the sunspot records made by Hevelius indicates that his reports of sunspots were true to the observations.

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Cited by in corpus (10)

• Re-calibration of the Sunspot Number: Status Report
• Strong evidence of low levels of solar activity during the Maunder Minimum
• Reanalyses of the Sunspot Observations of Fogelius and Siverus: Two "Long-Term" Observers during the Maunder Minimum
• Revisiting Christoph Scheiner's Sunspot Records: a New Perspective on Solar Activity of the Early Telescopic Era
• Number of Sunspot Groups from the Galileo-Scheiner controversy revisited
• Daniel Mögling's sunspot observations in 1626 - 1629: A manuscript reference for the solar activity before the Maunder Minimum
• Soonspot: Software to Determine Areas and Sunspot Positions
• On the use of naked-eye sunspot observations during the Maunder Minimum
• Long-lived sunspots in historical records: a case study analysis from 1660 to 1676
• An analysis of the solar differential rotation in solar cycle No. 19 (1954-1964) determined using Kanzelhoehe sunspot group positions