Solar Physics

, Volume 291, Issue 9–10, pp 3103–3122 | Cite as

70 Years of Sunspot Observations at the Kanzelhöhe Observatory: Systematic Study of Parameters Affecting the Derivation of the Relative Sunspot Number

  • Werner PötziEmail author
  • Astrid M. Veronig
  • Manuela Temmer
  • Dietmar J. Baumgartner
  • Heinrich Freislich
  • Heinz Strutzmann
Sunspot Number Recalibration


The Kanzelhöhe Observatory (KSO) was founded during World War II by the Deutsche Luftwaffe (German Airforce) as one station of a network of observatories that were set up to provide information on solar activity in order to better assess the actual conditions of the Earth’s ionosphere in terms of radio-wave propagation. Solar observations began in 1943 with photographs of the photosphere and drawings of sunspots, plage regions, and faculae, as well as patrol observations of the solar corona. At the beginning, all data were sent to Freiburg (Germany). After WW II, international cooperation was established and the data were sent to Zurich, Paris, Moscow, and Greenwich. Relative sunspot numbers have been derived since 1944. The agreement between relative sunspot numbers derived at KSO and the new International Sunspot Number (ISN) (SILSO World Data Center in International Sunspot Number Monthly Bulletin and online catalogue, 1945 – 2015) lies within \({\approx}\,10~\%\). However, revisiting the historical data, we also find periods with larger deviations. The reasons for the deviations were twofold: On the one hand, a major instrumental change took place during which the instrument was relocated and modified. On the other hand, a period of frequent replacements of personnel caused significant deviations; this clearly shows the importance of experienced observers. In the long term, the instrumental improvements led to better image quality. Additionally, we find a long-term trend towards better seeing conditions that began in 2000.


Solar cycle, Observations Sunspots, Statistics Instrumental effects Atmospheric seeing 



Many pieces of information about historical and instrumental details were not available in printed or written form. We are grateful to Hermann Haupt and Thomas Pettauer, who have shaped the observatory through their work since the early 1950s and 1960s, respectively, for all of the information that they provided us through private communications that would otherwise have been lost.

Disclosure of Potential Conflicts of Interest

The authors declare that they have no conflicts of interest.


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Copyright information

© Springer Science+Business Media Dordrecht 2016

Authors and Affiliations

  1. 1.Kanzelhöhe Observatory for Solar and Environmental ResearchUniversity of GrazGrazAustria
  2. 2.Institute of Physics/IGAMUniversity of GrazGrazAustria

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