Sunspot Observations Made by Hallaschka During the Dalton Minimum
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 so-called Dalton minimum, around the maximum phase of Solar Cycle 6. These records are very valuable because they allow us to complete observational gaps in the collection of sunspot group numbers, improving the 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. We conclude, however, that the 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 solar activity during the Dalton minimum.
KeywordsSolar Cycle, observations Sunspots, statistics
This research was supported by the Economy and Infrastructure Counselling of the Junta of Extremadura through project IB16127 and grant GR15137 (co-financed by the European Regional Development Fund) and by the Ministerio de Economía y Competitividad of the Spanish Government (AYA2014-57556-P and CGL2017-87917-P). RA acknowledges the support from Deutsche Forschungsgemeinschaft through grant AR355/12-1. The authors have benefited from the participation in the ISSI workshops. The authors acknowledge Rudolf Brazdil for his help in locating the original sunspot drawings of Hallaschka.
Disclosure of Potential Conflicts of Interest
The authors declare that they have no conflicts of interest.
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