Conflicts with astronomers
While Galileo was writing his book on floating in water, a book about sunspots was published pseudonymously by the German Jesuit Christopher Scheiner. Forbidden by his superior to risk discredit to his order, he wrote in the form of letters to Mark Welser of Augsburg, who had previously sent Galileo the German attack against lunar mountains. Welser, a banker to the Jesuits who was soon made a member of the Lincean Academy, printed Scheiner's letters under the name of ‘Apelles’ and sent them to Galileo for comment, remarking that he did not suppose sunspots were anything new to the Italian.
Galileo received this material on a visit to Florence to place his new book in the hands of a printer. His former pupil, a Benedictine abbot named Benedetto Castelli, had arrived to assist him and was asked to see the book through the press and to make daily observations of sunspots as carefully as possible. Castelli recorded those so accurately that the daily movement of a spot could be measured, enabling Galileo to prove that the spots must be on the sun's surface and that the sun rotated about once a month. Scheiner had concluded that what were called sunspots were really tiny planets revolving around the earth or the sun and obstructing our vision. He wrote additional letters which Welser printed, also answered by Galileo, whose three Letters on Sunspots were published at Rome in 1613 under the auspices of the Lincean Academy.