7.1 Sunspots  (Page 2/3)

Scheiner, a Jesuit mathematician at the university of Ingolstadt (near Augsburg), wished to preserve theperfection of the Sun and the heavens and therefore argued that sunspots were satellites of the Sun. They appeared as black spotswhen they passed in front of the Sun but were invisible at other points in their orbits. Their orbits had to be very close to theSun for their shapes were foreshortened as they approached its edge. Scheiner observed sunspots through a telescope equipped withcolored glasses.

In the winter of 1611-12, when Galileo received a copy of Scheiner's tract fromWelser along with a request for his comments, he was ill, and what little energy he had he was devoting to the publication of hisDiscourse on Bodies in Water. When, however, that book was at the printer's, in April 1612, he turned his attention to sunspots withthe help of his protege Benedetto Castelli , who was in Florence at the time. It was Castelli whodeveloped the method of projecting the Sun's image through the telescope, a technique that made it possible to study the Sun indetail even when it was high in the sky. Galileo wrote his first letter to Welser on sunspots, in which he argued that spots were,in fact, on the surface of the Sun or in its atmosphere, and although he could not say for certain what they were, theyappeared to him most like clouds.

While Scheiner wrote in Latin, Galileo wrote his letter in Italian, andWelser had to have it translated before Scheiner could read it. Scheiner had continued his solar observations, and by the timehe had mastered Galileo's letter he had already finished two more letters of his own to Welser. He now added a third, in which hecommented that his observations agreed precisely with those of Galileo and defended his judgment that sunspots were solarsatellites. This second series of letters was published by Welser in October 1612 under the title De Maculis Solaribus . . . Accuratior Disquisitio ("A More Accurate Disquisition . . . on Sunspots"). Scheiner maintained his pseudonym of Apelles"or, if you prefer, Odysseus under the shield of Ajax." In the meantime, Galileo had written a second letter to Welser in August1612. In this letter he showed a large number of sunspot observations, made at roughly the same time of the day, so thatthe Sun's orientation was the same and the motion of the spots across its disk could be easily followed. Upon receivingScheiner's second tract he wrote yet a third, dated December 1612, attacking Apelles's opinions once again. At the end of his lastletter Galileo mentioned the Copernican System favorably in a way that some scholars have interpreted as his first endorsement of that theory.

Galileo's three letters were published in Rome by the Lyncean Academy in the summer of 1613. About a third of the copies had reprints of thetwo tracts by Apelles (whose identity had in the meantime become known) in their original Latin. There was little doubt about thewinner of this contest. Scheiner's language was convoluted, and not only did Galileo demolish his argument, he also criticizedScheiner's a priori method of argument: the Sun is perfect, therefore it cannot have spots on its surface.

Up to this point, relations between Galileo and Scheiner were not strained. Scheiner had treated Galileo withgreat respect, and Galileo had been courteous in his language. Ten years later, in his Assayer, Galileo complained about those whowould steal his priority of discovery, mentioning the case of sunspots but not mentioning Scheiner. It is almost certain thatGalileo was complaining about several others who had published on sunspots but who had not recognized his priority. Scheiner, who atthis time was settling in Rome, took Galileo's complaint to be directed at him and became Galileo's sworn enemy.

Scheiner had in the meantime published several important books on optics, and he had continued his study of theSun. He published his results in a massive tome, Rosa Ursina, ("The Rose of Orsini"),

After this time, however, sunspot activity was drastically reduced. When, in 1671, a prominent sunspot wasobserved, it was treated as a rare event. Sunspot activity increased again after about 1710. The period of low activity isnow referred to as the Maunder Minimum, after Edward Walter Maunder (1851-1928), one of the first modern astronomers to studythe long-term cycles of sunspots. Modern studies of sunspots originated with the rise of astrophysics, around the turn of thecentury. The chief early investigator of these phenomena in the United States was George Ellery Hale (1868-1938), who built thefirst spectro-heliograph and built the Yerkes and Mount Wilson observatories, including the 200-inch telescope on PalomarMountain.