Sunspot Observations Made by Hallaschka During the Dalton Minimum

Abstract

We present and analyse the sunspot observations performed by Franz I. C. Hallaschka in 1814 and 1816. These solar observations were carried out during the socalled Dalton minimum, around the maximum phase of the Solar Cycle 6. These records are very valuable because they allow us to complete observational gaps in the collection of sunspot group numbers, improving its coverage for this epoch. We have analysed and compared the observations made by Hallaschka with the records made by other contemporary observers. Unfortunately, the analysis of the sunspot areas and positions showed that they are too inaccurate for scientific use. But, we conclude that sunspot counts made by Hallaschka are similar to those made by other astronomers of that time. The observations by Hallaschka confirm a low level of the solar activity during the Dalton minimum.

Sunspot and Group Number: Recent advances from historical data

“…Hayakawa et al (2018) recovered a sunspot drawing made by Iwahashi Zenbei on 26 August 1793 and Denig & McVaugh (2017) analyzed a set of 25 drawings made by Jonathan Fisher in 1816 and 1817. Carrasco et al (2018b) recovered the sunspot observations performed by Cassian Hallaschka in 1814 and 1816. These works have helped to improve our knowledge of solar activity for the Dalton minimum.…”

Thaddäus Derfflinger’s Sunspot Observations during 1802–1824: A Primary Reference to Understand the Dalton Minimum

“…) Thaddäus Derfflinger's sunspot observations during 1802-1824, The Astrophysical Journal, doi: 10.3847/1538 While Derfflinger experienced the turmoil during the French invasion under Napoleon in 1800 and 1804-1805 (Fellöcker, 1864, p. 96), he continued his sunspot observations even during the second invasion. He was in regular contact with observatories in Vienna and Prague, including with the contemporary sunspot observer Franz Hallaschka (Fellöcker, 1864, p. 99-100) whose sunspot records have been recently recovered (Carrasco et al, 2018). During the last two decades of Derfflinger life, he suffered from the degradation of his eyesight and lost his left eyesight in spring 1819 (Fellöcker, 1864, p. 92).…”

“…Excluding the apparent spotless days, we have also revised 7 observational dates, eliminated 8 observational dates, and added 7 observational dates against the register in the existing dataset (Hoyt and Schatten, 1998;Vaquero et al, 2016) and additional sunspot observations by Fisher (Denig and McVaugh, 2017) and Hallaschka (Carrasco et al, 2018). Hoyt and Schatten, 1998;Vaquero et al, 2016).…”

“…Revised sunspot group number of Derfflinger (blue diamond in the summary manuscript and red cross in the logbooks) contextualized upon the sunspot group number of the existing observers (black dot:Vaquero et al, 2016) and additional sunspot observations by Fisher (gray triangle:Denig and McVaugh, 2017) and Hallaschka (green triangle:Carrasco et al, 2018).InFigure 5, we have incorporated the sunspot group number in Derfflinger's summary manuscript and logbook as they are and contextualised them upon the existing sunspot group number by) Thaddäus Derfflinger's sunspot observations during 1802-1824, The Astrophysical Journal, doi: 10.3847/1538 contemporary observers. The summary manuscript and logbooks occasionally provide observations with different group number and observations on different days.…”

The effect of telescope aperture, scattered light and human vision on early measurements of sunspot and group numbers

“…In their turn, sunspot area is a much more robust measure than SSN and GN. However, while sunspot areas could be derived even from the very early drawings, they might be a subject of large uncertainties due to different drawing styles, lack of proper scaling, and some may even be unsuitable for a scientific use (e.g., Arlt et al 2016;Senthamizh Pavai et al 2015;Carrasco et al 2018b;Fujiyama et al 2019).…”