page_title: Letters on Sunspots
section_title: Critical dialogue with Scheiner
hierarchical_section_title: Letters on Sunspots / Critical dialogue with Scheiner
caption_attribution_description: Markus Welser (1558–1614), Kupferstich 19 x 13 Centimeter, Umschrift: „Marcus Velserus S. Cæs. Majest. A. Consiliis, Undecimus Reip. August. Duumvir", in den vier Ecken die Wappen der Welser, Pimmel, Baumgartner und Honold. Nr. XI. in der Sockelleiste.
context_page_description: Letters on Sunspots was a pamphlet written by Galileo Galilei in 1612 and published in Rome by the Accademia dei Lincei in 1613. In it, Galileo outlined his recent observation of dark spots on the face of the Sun. His claims were significant in undermining the traditional Aristotelian view that the Sun was both unflawed and unmoving.
  The Letters on Sunspots, was a continuation of Sidereus Nuncius, Galileo's first work where he publicly declared that he believed that the Copernican system was correct. This was the first work where Galileo used a ship, which would later become famous in Dialogue Concerning the Two Chief World Systems.
  Galileo often mentions how he does not know or understand some things. He mentions that the Sun might not be revolving, or that the spots might look different if they were viewed in different parts of the world. However, in one passage, he states that the Sun does have a motion, and he wonders what causes this motion. This is where his work established a connection between cosmology and mechanics. Galileo wrote, "I seem to have observed that physical bodies have physical inclination to some motion."
context_section_description: When Jesuit Christoph Scheiner first observed sunspots in March 1611, he ignored them until he saw them again in October. When he saw them again, he attributed the sightings to either a defect in the eye, problems with the lens of the telescope, or a possible disturbance in the atmosphere, but he rejected all three hypotheses. He rejected the hypothesis that he had a defect in his eye because others also observed the spots. He used eight other telescopes and all of them had visible spots on the Sun. He also rejected that there was a disturbance in the atmosphere for four reasons.The first was that no cloud could follow the Sun's diurnal motion throughout the day, especially given the Sun's diameter. The spots also showed no parallel motion, but the spot's movement across the Sun was constant. His final reason was that the spots could be seen through small clouds. Scheiner believed that these dark spots were visible because there were small orbiting bodies around the Sun, which would block the sun's light. This explanation would allow him to avoid Aristotle's belief that the Sun was a perfect celestial being.
  Then, under the pseudonym Apelles latens post tabulam (Apelles hiding behind the painting),  he presented his description and conclusions about them in three letters to the Augsburg banker and scholar Mark Welser. Scheiner wanted to remain anonymous, because he believed in order to avoid involving the Jesuit order and the church generally in an area of controversy. Welser published them on his own presses, sent copies to astronomers around Europe, and invited them to reply. It was Welser's invitation which prompted Galileo to reply with two letters, arguing that the sunspots were not satellites, as Scheiner ('Apelles') maintained, but were features either on the Sun's surface or just above it.
  In the meantime, Scheiner sent Welser two further letters on the subject, and after he had read Galileo's first letter, he responded with a sixth of his own. These later letters were different in tone to the first three, as they hinted that Galileo was claiming credit for having discovered the phases of Venus, when in fact proper credit was due to others. They also implied that Galileo had copied Scheiner's helioscope in order to do his research.
  Having published Scheiner's first three letters under the title Tres Epistolae de Maculis Solaribus ("Three Letters on Solar Spots"), Welser now published his second three, also in 1612, as De Maculis Solaribus et Stellis circa Iovis Errantibus Accuratior Disquisition ("A More Accurate Disquisition Concerning Solar Spots and Stars Wandering around Jupiter"). Having read these second three letters, Galileo replied with a third of his own, much sharper and more polemical in tone than his earlier ones. Welser declined to publish Galileo's letters, perhaps because of the sarcastic tone they took towards Apelles, although the reason he gave Galileo was the exorbitant cost of producing all the illustrations Galileo wanted.
caption: Mark Welser
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