Stephan Prantner's Sunspot Observations during the Dalton Minimum

TL;DR

This study uncovers and analyzes Stephan Prantner's detailed sunspot observations from 1804-1844, providing new data that enhances understanding of solar activity during the Dalton Minimum and its comparison to other solar cycles.

Contribution

The paper presents previously unknown, detailed sunspot observations from Prantner, doubling the existing data and offering new insights into solar activity during the Dalton Minimum.

Findings

Prantner's observations cover 215 days, more than previous estimates.

Sunspot counts ranged up to 7-9 groups per day.

Sunspot distribution shows hemispheric activity, contrasting with the Maunder Minimum.

Abstract

In addition to regular Schwabe cycles (~ 11 years), solar activity also shows longer periods of enhanced or reduced activity. Of these, reconstructions of the Dalton Minimum provide controversial sunspot group numbers and limited sunspot positions, partially due to limited source record accessibility. We analysed Stephan Prantner's sunspot observations from 1804--1844, the values of which had only been known through estimates despite their notable chronological coverage during the Dalton Minimum. We identified his original manuscript in Stiftsarchiv Wilten, near Innsbruck, Austria. We reviewed his biography (1782--1873) and located his observational sites at Wilten and Waidring, which housed the principal telescopes for his early and late observations: a 3.5-inch astronomical telescope and a Reichenbach 4-feet achromatic erecting telescope, respectively. We identified 215 days of datable sunspot observations, which are twice as much data as his estimated data in the existing database (= 115 days). Prantner counted up to 7--9 sunspot groups per day and measured sunspot positions, which show their distributions in both solar hemispheres. These results strikingly emphasise the difference between the Dalton Minimum and the Maunder Minimum as well as the similarity between the Dalton Minimum and the modern solar cycles.