Thaddäus Derfflinger's sunspot observations during 1802-1824: A primary reference to understand the Dalton Minimum

Abstract

As we are heading towards the next solar cycle, presumably with a relatively small amplitude, it is of significant interest to reconstruct and describe the past grand minima on the basis of actual observations of the time. The Dalton Minimum is often considered one of the grand minima captured in the coverage of telescopic observations. Nevertheless, the reconstructions of the sunspot group number vary significantly, and the existing butterfly diagrams have a large data gap during the period. This is partially because most long-term observations have remained unexplored in historical archives. Therefore, to improve our understanding on the Dalton Minimum, we have located two series of Thaddäus Derfflinger's observational records (a summary manuscript and logbooks) as well as his Brander's 5.5-feet azimuthal-quadrant preserved in the Kremsmünster Observatory. We have revised the existing Derfflinger's sunspot group number with Waldmeier classification and eliminated all the existing 'spotless days' to remove contaminations from solar meridian observations. We have reconstructed the butterfly diagram on the basis of his observations and illustrated sunspot distributions in both solar hemispheres. Our article aims to revise the trend of Derfflinger's sunspot group number and to bridge a data gap of the existing butterfly diagrams around the Dalton Minimum. Our results confirm that the Dalton Minimum is significantly different from the Maunder Minimum, both in terms of cycle amplitudes and sunspot distributions. Therefore, the Dalton Minimum is more likely a secular minimum in the long-term solar activity, while further investigations for the observations at that time are required.

main text 17 pages, references 7 pages, and 8 figures; accepted for publication in the ApJ

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Cited by in corpus (12)

• Robustness of Solar-Cycle Empirical Rules Across Different Series Including an Updated ADF Sunspot Group Series
• The Dalton Minimum and John Dalton's Auroral Observations
• Strong evidence of low levels of solar activity during the Maunder Minimum
• Scrutinizing the relationship between plage areas and sunspot areas and numbers
• Reanalyses of the Sunspot Observations of Fogelius and Siverus: Two "Long-Term" Observers during the Maunder Minimum
• The Solar Corona during the Total Eclipse on 16 June 1806: Graphical Evidence of the Coronal Structure during the Dalton Minimum
• Daniel Mögling's sunspot observations in 1626 - 1629: A manuscript reference for the solar activity before the Maunder Minimum
• Candidate Auroral Observations during the Major Solar-Terrestrial Storm in May 1680: Implication for Space Weather Events during the Maunder Minimum
• Revisiting the Amplitude of Solar Cycle 9: The Case of Sunspot Observations by W.C. Bond
• Sunspot positions from observations by Flaugergues in the Dalton Minimum
• Sunspot Records by Antonio Colla just after the Dalton Minimum
• Long-lived sunspots in historical records: a case study analysis from 1660 to 1676