Abstract
We have examined the more than 1100 drawings of the solar disk made by the German amateur astronomer Johann Caspar Staudach during 1749 – 1799 and counted the spots on each image. Using the modern perception of how to group spots into active regions, we regrouped the spots as a modern observer would. The resulting number of groups was found to be higher on average by 25 % than the first count of groups performed by Wolf in 1857, which was used by Hoyt and Schatten (Solar Phys. 181, 491, 1998) in their construction of the group sunspot number. Compared to other observers at the time, Staudach’s drawings have a very low average number, about two, of spots per group, possibly indicating an inferior telescope that probably suffered from spherical and chromatic aberration, as would be typical of amateur telescopes of the day. We have initiated an ongoing project aiming at observing sunspots with antique telescopes having similar defects in order to determine the factor necessary to bring the Staudach observations onto a modern scale.
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20 December 2016
An erratum to this article has been published.
References
Arlt, R.: 2008, Digitization of sunspot drawings by Staudacher in 1749 – 1796. Solar Phys. 247, 399. DOI .
Clette, F., Svalgaard, L., Vaquero, J.M., Cliver, E.W.: 2014, Revisiting the sunspot number: A 400-year perspective on the solar cycle. Space Sci. Rev. 16, 35. DOI .
Haase, C.: 1869, Besprechung der Beobachtungen Staudachers. In: Zeitschrift für populäre Mittheilungen aus dem Gebiet der Astronomie und verwandter Wissenschaften 3, 51. babel.hathitrust.org/cgi/pt?id=chi.73241168;view=1up;seq=580 , downloaded 08 November 2016.
Hoyt, D.V., Schatten, K.H.: 1995, A new interpretation of Christian Horrebow’s sunspot observations from 1761 to 1777. Solar Phys. 160, 387. DOI .
Hoyt, D.V., Schatten, K.H.: 1998, Group sunspot numbers: A new solar activity reconstruction. Solar Phys. 181, 491. DOI .
Spörer, G.: 1887, In: Letter to Wolf in Mittheilungen über die Sonnenflecken LXIX, item 547.
Svalgaard, L., Schatten, K.H.: 2016, Reconstruction of the sunspot group number: The backbone method. Solar Phys. 291, 2653. DOI .
Waldmeier, M.: 1938, Chromosphärische Eruptionen. Z. Astrophys. 16, 276.
Woeckel, L.: 1846, Die Sonne und ihre Flecken, Campe, Nürnberg. download.digitale-sammlungen.de/pdf/1445541475bsb10049284.pdf .
Wolf, R.: 1857, Mittheilungen über die Sonnenflecken IV, 52.
Wolf, R.: 1858, Mittheilungen über die Sonnenflecken VII, 160.
Wolf, R.: 1859, Mittheilungen über die Sonnenflecken IX, 208.
Wolf, R.: 1861, Mittheilungen über die Sonnenflecken XIII, 83.
Wolf, R.: 1865, Mittheilungen über die Sonnenflecken XIX, 263.
Wolf, R.: 1870, Mittheilungen über die Sonnenflecken XXVII, 239.
Wolf, R.: 1873, Mittheilungen über die Sonnenflecken XXXIII, 120.
Acknowledgments
We thank Rainer Arlt for making available the photographic images of the Staudach drawings. L. Svalgaard thanks Stanford University for continuing support.
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Sunspot Number Recalibration
Guest Editors: F. Clette, E.W. Cliver, L. Lefèvre, J.M. Vaquero, and L. Svalgaard
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Svalgaard, L. A Recount of Sunspot Groups on Staudach’s Drawings. Sol Phys 292, 4 (2017). https://doi.org/10.1007/s11207-016-1023-x
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DOI: https://doi.org/10.1007/s11207-016-1023-x