Sunspot Positions and Areas from Observations by Galileo Galilei

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11 Scopus citations


Sunspot records in the seventeenth century provide important information on the solar activity before the Maunder minimum, yielding reliable sunspot indices and the solar butterfly diagram. Galilei’s letters to Cardinal Francesco Barberini and Marcus Welser contain daily solar observations on 3 – 11 May, 2 June – 8 July, and 19 – 21 August 1612. These historical archives do not provide the time of observation, which results in uncertainty in the sunspot coordinates. To obtain them, we present a method that minimizes the discrepancy between the sunspot latitudes. We provide areas and heliographic coordinates of 82 sunspot groups. In contrast to Sheiner’s butterfly diagram, we found only one sunspot group near the Equator. This provides a higher reliability of Galilei’s drawings. Large sunspot groups are found to emerge at the same longitude in the northern hemisphere from 3 May to 21 August, which indicates an active longitude.

Original languageEnglish
Article number31
Number of pages21
JournalSolar Physics
Issue number2
StatePublished - Feb 2018

Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


  • Solar cycle, observations
  • Sun: activity
  • Sunspots


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