Popular Science Monthly/Volume 51/September 1897/The Discovery of the Sun Spots
|THE DISCOVERY OF THE SUN SPOTS.|
By M. A. LANCASTER.
SPOTS or groups of spots were seen more or less distinctly upon the sun previous to the invention of the telescope. The observations are described under various forms, first among which may be mentioned obfuscations or obscurations of the sun. At other times they were believed to be passages of Mercury in front of the sun, as in 807, a date mentioned by the historians of Charlemagne, and on the 28th of May, 1607, when even Kepler was deceived. In 859 Alkindi thought he observed a transit of Venus; but the black object he saw on the sun's disk was only a spot large enough to be perceived by the naked eye.
Observations of obscurities or spots on the sun have been made in China at different epochs, the most ancient one dating from the year 301. Between that date and the beginning of the thirteenth century the great Encyclopædia of Matouan-lin contains forty-five mentions of the phenomenon. The existence of dark spots on the sun was recognized very anciently by the aborigines of Peru. The Arabs have recorded prolonged observations of the disk of the sun, among which are those of 535 and 626.
The oldest mention of a sun spot in Europe, a spot which was supposed to be Mercury, is by an anonymous chronicler of the eighth century. Different observations of sun spots before the invention of the telescope are recorded in Zach's Monatliche Correspondenz, vol. xv, 1807, and in Humboldt's Cosmos, vol. iii.
The new instrument, invented in Holland, first permitted the scientific study of the solar surface. Galileo appears to have seen the spots on the sun for the first time in October, 1610, but did not account for the nature of the phenomenon. Jean Fabricius may have remarked the spots toward the end of the year 1610, and certainly observed them in March, 1611. Scheiner reported his discovery of the spots in April, 1611, but did not account for what he saw. Harriott, who is believed by Zach to have seen the spots as early as December, 1610, and whose manuscripts have been examined by Rigaud, did not really see them till early in December, 1611, and comes, consequently, only fourth in the order of priority.
There have been lively controversies at different times concerning the claims of these three astronomers to priority in the discovery of the sun spots. The discussions were summarized by Arago in an article published in l'Annuaire du Bureau des Longitudes in 1842. The question has been settled by deciding that Galileo first saw the spots with the aid of the telescope, but that Fabricius first announced their existence to the scientific world and pointed out their nature. The texts were plain enough on this point, and the discussion was prolonged more by the agitation of questions concerning the meaning of words than by any need of clearing up the facts.
A work recently published by Dr. Gerhard Berthold on Fabricius contains a number of previously unpublished documents, and throws light on some obscure points in the history of astronomy at the beginning of the seventeenth century.
An interesting analysis of this essay has been published by M. E. Millosevich in the Atti of the Accademia dei Lincei of Rome. While its main object is to establish the claim of Jean Fabricius to priority in the discovery of the sun spots, it further furnishes many facts previously unknown in the life of this astronomer and of his father, David Fabricius. The claim of priority having been already settled by Humboldt, the secondary object is really the more important one. A little-known paper of Jean Fabricius on sun spots and their apparent turning with the sun, published at Wittenberg in 1611, is reproduced in the book; and after it a wholly unknown astrological paper by David Fabricius on the appearance of the new star in Ophiucus, which Kepler's pupil, Jean Brunowski, discovered on the 10th of December, 1604. David Fabricius saw this star for the first time December 13, 1604, or only three days after Brunowski, of whose discovery he certainly knew nothing, and wrote two other notices of it, which are lost. The frontispiece of David Fabricius's Prognosticon astronomicum is also given, with a complete list of the author's writings, including those which are lost. Of these, the Prognostica for 1607 and 1616 have recently been found at Darmstadt and Nuremberg. From a few facts concerning the life of David Fabricius gleaned from the Prognosticon for 1617, it appears that he was born at Essen, in East Friesland, March 9, 1564, and died—killed with a spade by a peasant of his commune—May 7, 1617. He assumed the ecclesiastical dress at an early age, and performed the offices of a court pastor, while he also devoted himself to astronomical studies, and was the first to announce that Omicron or Mira Ceti, was a variable star. He made this discovery August 13, 1596, and on the same day remarked a star of the third magnitude, red like Mars, and situated in 25° 47′ and 15° 45′ south of the ecliptic. Twelve years passed without his seeing it only very indistinctly, and he did not find it again clearly till 1609. The author observes that the astrological intimations of David Fabricius did not prevent his being a good astronomer of the second rank, like Longomontanus, Scheiner, and Simon Marius. His correspondence with Kepler proves that he furnished him with important material for the composition of his works.
Jean Fabricius, the eldest of seven sons, was born at Resterhave, near Dornum, in East Friesland, January 18, 1587. The Calendarium historicum of David Fabricius gives some facts concerning his life. He attended the university at Helmstadt as a medical student in 1605, at Wittenberg in the next year, whence he passed to Leyden, where he was registered as a student of medicine in 1609. Omitting certain statements concerning his astrological and meteorological studies, we remark that the publication of the work to which he owes his fame in astronomy dates from the time of his doctorate in philosophy at Wittenberg, whither he returned after his sojourn at Leyden. The telescope was discovered in Holland in 1608 by the optician Jean Lippersheim, of Middelbourg, who immediately applied to the States General for a patent. Jean Fabricius learned of the discovery at Leyden, and took the instrument to Osteel, where his father was, and with it found the sun spots. Nothing is known of him after the publication of the book on the sun spots already mentioned (1611), except that he practiced medicine at Marienhave, near Osteel, and died there probably about 1617. If the Prognosticon for 1618 had not been lost, we should doubtless have had some details respecting his death. In the lack of other sources of knowledge, there is left us the eulogy addressed by Kepler to David Fabrcius: "But also reading in your Prognosticon for the year 1618, by which I am better informed concerning his [Jean's] too early death," etc.; and further on, "But, indeed, there is this excellent little book concerning the solar spots in the year 1611," etc. The author gives particulars concerning the first day of the discovery, the method of observation by projection, and the conclusions which Jean, aided by his father's advice, drew (spots fixed in the body of the sun) concerning the sun's rotation around an axis. Neither the Narration nor the writings of David, so far as they are known to us, give any hints concerning the exact date of the discovery, so that we were confined to guesses till M. Berthold found the Prognosticon of David for 1615, which gave the 27th of February (9th of March N. S.), 1611, as the exact date of the event. Furthermore, a letter from David to Maestlin says that the Narration appeared at the time of the autumn fair of 1611, and this is confirmed by Kepler.
At this point in his learned essay Dr. Berthold discusses the question of priority, for which a claim was earnestly pressed as against Galileo by the Jesuit Scheiner, who assumed the name of Apelles. It is really very singular, as it appears to the author, that not a word was said of Jean Fabricius in this controversy, and it might be inferred that both contestants alike knew nothing of the Narration, but for certain considerations and facts adduced by Dr. Berthold which make this supposition exceedingly improbable, if not impossible.
It is proper to observe here that after the telescope was invented all the discoveries in celestial objects became, as it were, matters of course, and that, whatever noise might be made about them at first, the merit of the observers is insignificant in comparison with that of the calculators who knew how to reason out the basis of the true system. Even if it should be proved that Galileo learned of the existence of the spots from Fabricius's Narration, or from the letters of the false Apelles, the remarkable fact remains that in his first reply to Welser he corrects the errors in the reasoning of Apelles concerning the direction of the sun's rotation.
In Mario Welser's first letter to Galileo, dated January 6, 1612, he asks Galileo's opinion concerning the spots discovered by Scheiner, and forwards three of the latter's famous letters. Three months afterward (May 4, 1612) Galileo answers him in a very long letter, saying that he has been observing the spots for eighteen months, that he has shown them to several friends, and has besides within a year exhibited them to many prelates and lords at Rome. According to this, he must have seen the spots as early as the end of November, 1610; and the discovery, or first observation, must have been as early as the summer of 1610, or before Galileo removed from Venice to Florence, the change of residence taking place at the end of August, 1610. It is proved, in fact, by a letter from the friar Fulgence Servita, a theologian of the Most Serene Republic, that he showed the spots to Father Paolo. It is not easy to divine why Galileo, usually so careful of his rights, did not this time make a claim for priority in discovery; but it may be supposed that by the side of the discovery of the Medici stars, Saturn's rings, and the phases of Venus, that of dark points on the sun, changing in character and disappearing according to the position of the star, appeared of trifling importance to him; and this is to a certain extent confirmed by the reply to Welser. Galileo's observations, in fact, did not begin to be known till in 1612; and if we did not trust to his assertions or to ocular testimony, Fabricius, Scheiner, and perhaps others, made the discovery before him; but this would not be a fair judgment. It must be admitted that Galileo first observed the spots on the sun with the aid of the Lippersheim glass; but his earliest notices on the subject did not appear till the spring of 1612, while the earliest publication on it is that of Fabricius, who discovered the spots on March 9, 1611, in complete ignorance that Galileo had observed them eight months before.
The false Apelles pretended that he had observed the spots for the first time, together with one of his pupils, in March, 1611. How, then, could Kepler have written to David Fabricius of "the sun spots seen by your son long before, Apelles," if, as we know now, Jean discovered them in March, 1611? No one was more in the current of events than Kepler, and he was astonished at the letters of Apelles. Besides, Scheiner told Welser that he had observed some darkish things on the sun, but attached no importance to them till October, when he resumed his observations—that is, after Jean Fabricius's book had been published.
It finally appears from Dr. Berthold's book that (1) Galileo was the first to observe the spots on the sun with the Lippersheim telescope in the summer of 1610, but he did not publish his drawings and observations till the spring of 1613, At that time he was master enough of the question of the sun's rotation to correct Scheiner's errors. (2) Jean Fabricius discovered the sun spots on March 9, 1611; he was acquainted with the sun's rotation, and was the first to publish a work on the subject. His discovery is quite independent of any previous suggestion. (3) Scheiner may also have observed the sun spots independently in March, 1611, but he attached no importance to them till October of the same year, after the publication of the Narration by Fabricius. His merit consists in his having continued the observations, and in having collected a large number of them, which were inserted in his Rosa Ursina.
The "long before" (longe ante) of Kepler is unexplained.—Translated for the Popular Science Monthly from Ciel et Terre.
- These facts and dates are from Houzeau's Vade-mecum of Astronomy.
- Der Magister Johann Fabricuius und die Sonnenflecken.
- The period of the variability of this star was determined by Jean Holward, forty-two years afterward.