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Sunspot group tilt angle measurements from historical observations

By V. Senthamizh Pavai, R. Arlt, A. Diercke, C. Denker and J. M. Vaquero

Abstract

Sunspot positions from various historical sets of solar drawings are analysed with respect to the tilt angles of bipolar sunspot groups. Data by Scheiner, Hevelius, Staudacher, Zucconi, Schwabe, and Spoerer deliver a series of average tilt angles spanning a period of 270 years, additional to previously found values for 20th-century data obtained by other authors. We find that the average tilt angles before the Maunder minimum were not significantly different from the modern values. However, the average tilt angles of a period 50 years after the Maunder minimum, namely for cycles 0 and 1, were much lower and near zero. The normal tilt angles before the Maunder minimum suggest that it was not abnormally low tilt angles which drove the solar cycle into a grand minimum.Comment: accepted by Advances in Space Researc

Topics: Astrophysics - Solar and Stellar Astrophysics
Publisher: 'Elsevier BV'
Year: 2016
DOI identifier: 10.1016/j.asr.2016.03.002
OAI identifier: oai:arXiv.org:1603.02510

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