Early Observations of Sunspots: Scheiner and Galileo

  • Article
  • 18 pages
  • Level: university

A 1997 article by Juan Casanovas, S. J., an astronomer with the Vatican Observatory, published in 1st Advances in Solar Physics Euroconference – Advances in Physics of Sunspots:

Abstract: There had been occasional observations of spots on the Sun since antiquity. Kepler observed a sunspot in 1607 but he interpreted it as a Mercury’s transit. One year after the introduction of the telescope astronomers identified spots on the Sun. J. Fabricius was the first to print a book on sunspots at the end of 1611, but this book had little diffusion. Fabricius rightly thought that the spots belonged to the Sun. The Jesuit C. Scheiner independently observed sunspots on the Sun and he announced his discovery at the end of 1611 in three letters under the pseudonym Apelles. Scheiner failed to observe the returning of the spots and hence did not recognize the solar rotation. Therefore he preferred to see the spots as caused by little bodies orbiting the Sun. Based on Scheiner’s observations, Kepler concluded that the spots were on the solar surface like dross floating on melted metal. When Scheiner’s letters reached Italy, Galileo claimed to have observed sunspots much earlier, but if this had been the case, he had not published anything on sunspots. Galileo replied to Apelles’ letters affirming that the spots were on the surface of the Sun, like clouds. A bitter and long fight followed between Galileo and Scheiner on the priority of discovery. Techniques for solar observation progressed quickly. The solar image was observed projected on a white paper for measurement of sunspots positions. Scheiner later perfected this method installing the telescope on an equatorial mounting. Scheiner made over 2000 solar observations and determined the orientation of the solar axis of rotation. His methods and results were presented in his monumental work Rosa Ursina.

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