In a book published by the Academy of the Lynx, the Jesuit astronomer Christoph Scheiner argued that sunspots are little planets circling the Sun like. Galileo’s sunspot letters to Mark Welser. Introduction. Galileo’s letters on sunspots were written to Mark Welser in , and published in Galileo Galilei. How did Galileo prove the sunspots were actually on the Sun? > rate, the letters represent positions of a sunspot at equal intervals of time.

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Sunspots are dark areas of irregular shape on the surface of the Sun. Their short-term and long-term cyclical nature has been established in the past century. Spots are often big enough to be seen with the naked eye. While direct observation of the Sun in a clear sky is painful and dangerous, it is feasible when the Sun is close to the horizon or when it is covered by a thin veil of clouds or mist.

Records of naked-eye sunspot observations in China go back to at least 28 BCE. In the West, the record is much more problematical. It is possible that the Greek philosopher Anaxagoras observed a spot in BCE, and it appears that there are a few scattered mentions in the ancient literature as well.

However, in the dominant Aristotelian cosmology, the heavens were thought to be perfect and unchanging. A spot that comes and goes on the Sun would mean that there is change in the heavens. Given this theoretical predisposition, the difficulty of observing the Sun, and the cyclic nature of spots, it is little wonder that records of sunspots are almost non-existent in Europe before the seventeenth century. A very large spot seen for no less than eight days in was simply interpreted as a passage of Mercury in front of the Sun.

Other mentions of spots seen on the Sun were ignored by the astronomers and philosophers. In Johannes Kepler wished to observe a predicted transit of Mercury across the Sun’s disk, and on the appointed day he projected the Sun’s image through a small hole in the roof of his house a camera obscura and did indeed observe a black spot that he interpreted to be Mercury.

Had he been able to follow up on his observation the next day, he would still have seen the spot. Since he knew that Mercury takes only a few hours to cross the Sun’s disk during one of its infrequent transits, he would have known that what he observed could not have been Mercury.

A sunspot [click for larger image] The scientific study of sunspots in the West began after the telescope had been brought into astronomy in Although there is still some controversy about when and by whom sunspots were first observed through the telescope, we can say that Galileo and Thomas Harriot were the first, around the end of ; that Johannes and David Fabricius and Christoph Scheiner first observed them in Marchand that Johannes Fabricius was the first to publish on them.

His book, De Maculis in Sole Observatis “On the Spots Observed in the Sun” appeared in the autumn ofbut it remained unknown to the other observers for some time. But although some of his corespondents began making regular observations a few months later, Galileo himself did not undertake a study of sunspots until April Scheiner began his serious study of spots in October and his first tract on the subject, Tres Epistolae de Maculis Solaribus Scriptae ad Marcum Welserum “Three Letters on Solar Spots written to Leters Welser ” appeared in January under the pseudonym “Apelles latens post galilleo or “Apelles waiting behind the painting.


Sunspot plate from Scheiner’s Tres Epistolae. They appeared as black spots when they passed in front of the Sun but were invisible at om points in their orbits.

Their orbits had to be very close to the Sun for their shapes were foreshortened as they approached its edge. Scheiner observed sunspots through a telescope equipped with colored glasses.

In the winter ofwhen Galileo received a copy of Scheiner’s tract from Zunspots along with a request for his comments, talileo was ill, and what little energy he had he was devoting to the publication of his Discourse on Bodies sunspohs Water. It was Castelli who developed the method of projecting the Sun’s image through the telescope, a technique that made it possible to study the Sun in detail 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 lettrrs surface of the Sun or in its atmosphere, and although he could not say for certain what they were, they appeared to him most like clouds.

While Scheiner wrote in Latin, Galileo wrote his letter in Italian, and Welser had to have it translated before Scheiner could read it. Scheiner had continued his oetters observations, and by the time he had mastered Galileo’s letter he had already finished two more letters of his own to Welser. He now added a third, in which he commented that his observations agreed precisely with those of Galileo and defended his judgment that sunspots were solar satellites.

This second series of letters was published by Welser in October under the title De Maculis Solaribus. Scheiner maintained his pseudonym of Apelles “or, if you prefer, Odysseus under the shield of Ajax.

Letters on Sunspots – Wikipedia

In this letter he showed a large number of sunspot observations, made at roughly the same time of the day, so that the Sun’s orientation was the same and the motion of the spots across its disk could be easily followed, as is shown in the sequence here. Upon receiving Scheiner’s second tract he wrote yet a third, dated Decemberattacking Apelles’s opinions subspots again. At the sunspofs of his last letter 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 About a third of the copies had reprints of the two tracts by Apelles whose identity had in the meantime become known in their original Latin.

There was little doubt about the winner of this contest. Scheiner’s language was convoluted, and not only did Galileo demolish his argument, he also criticized Scheiner’s a priori method of argument: Up to this point, relations between Galileo and Scheiner were not strained.


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Scheiner had treated Galileo with great respect, and Galileo sunapots been courteous in his language. Ten years later, in his AssayerGalileo complained about those who would steal his priority of discovery, mentioning the case of sunspots but not mentioning Scheiner. It is almost certain that Galileo was complaining about several others who had published on sunspots but who had not recognized his priority.

Scheiner, who at this time was settling in Rome, took Galileo’s complaint to be directed at him and became Galileo’s sworn enemy. Sunspot drawings from Scheiner’s Rosa Ursina.

He published his results in a massive tome, Rosa Ursina”The Rose of Orsini”[2] which became the standard treatise on sunspots for over a century. Scheiner had abandoned his opinion that spots were solar satellites, and he indeed came out in favor of the system of Tycho Brahe and abandoned the perfection of the heavens. His method of illustrating the motion of individual spots across the face of the Sun became the standard way of rendering this motion and the changing shapes of the spots.

Sunspot drawing by Gassendi. There is, therefore, a reasonably good sunspot record for the years After this time, however, sunspot activity was drastically reduced. When, ina prominent sunspot was observed, it was treated as a rare event.

Sunspot activity increased again after about Sunsoots period of low activity is now referred to as the Maunder Minimum, after Gallileo Walter Maunderone of sunsots first modern astronomers to study the long-term cycles of sunspots.

Modern studies of sunspots originated with the rise of astrophysics, around the turn of the century. The chief early investigator of these phenomena in the United States was George Ellery Halewho built the first spectro-heliograph and built the Yerkes and Mount Wilson observatories, including the inch telescope on Palomar Mountain. When a shoemaker praised the way Apelles had rendered shoes in the painting, Apelles revealed himself and thanked the shoemaker for the compliment, but this man now proceeded to give his not so complimentary opinions about other aspects of the painting.

Apelles answered “Let the shoemaker stick to his last.

On solar activity in the early seventeenth century, see D. Doubleday,pp. Personality, Tradition and Revolution Ann Arbor: University of Michigan Press,pp. Rhetoric and Science in the Copernican Controversy Chicago: University of Chicago Press, Thomas Harriot: Clarendon Press,pp. Sunspot plate from Scheiner: Helioscopium and sunspot images: Christoph Scheiner, Rosa Ursina Sunspot drawings by Gassendi: Pierre Gassendi, Opera Omnium6 vols.

Lyon,vol. Sunspot drawings by Hevelius: Johannes Hevelius, Selenographia We will not answer copyright requests. See the copyright page for more information. Sunspots drawings by Hevelius.