Analysis of the Sunspot Observations by Gustav Sporer in 1861–1893

Diercke Andrea, Humboldt-Universitat zu Berlin
Arlt Rainer, Leibniz-Institut fur Astrophysik, Potsdam
Denker Carsten, cdenker@aip.de Leibniz-Institut fur Astrophysik, Potsdam, Germany

Abstract
Much of our knowledge about the solar dynamo is based on sunspot observations. It is thus desirable to extend the set of positional and size data of sunspots into the past. Gustav Sporer observed in Germany from Anklam (1861–1873) and Potsdam (1874–1893). He left detailed drawings of sunspot groups, which were digitized and processed to mitigate artifacts left in the drawing by the passage of time. After careful geometrical correction, the sunspot data are now available as synoptic charts for more than 400 solar rotation periods. Individual sunspot positions can thus be precisely determined and spot areas can be accurately measured using morphological image processing techniques. These methods also allow us to determine tilts angles of active regions (Joy’s law) and to assess the complexity of an active region.