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On the name of the satellites of Jupiter discovered by Galileo
Miguel de Cervantes died in 1616 a pauper. He is buried in the convent Trinitarians nuns in Madrid, where there is a search now underway for his tomb. As well as his monumental work Don Quixote, which he himself considered the first modern novel, his extensive literary production included poetry and theater. It also appears that his scientific culture must have been considerable, as he kept in touch with the advances that were made at the start of the 17th century following the invention of the telescope. It is even possible that he made a significant scientific contribution naming the satellites of the planet Jupiter, which were identified when Galileo Galilei, the astronomer from Pisa, pointed the new instrument to the sky.
With the publication of “Sidereus Nuncius” (the Sidereal Messenger) in March 1610, Galileo began a real revolution, not only in astronomy but also in philosophy. He presented solid evidence overturning the interpretations of the world that had been firmly in place for centuries. In his work Galileo shows us an irregular and imperfect moon; he identifies a large number of new stars that are weaker than those seen with the naked eye; he reveals the complex nature of the Milky Way; and he discovers four bodies orbiting Jupiter, delivering a devastating blow to the Ptolemaic cosmology. In successive letters he continued his demolition of the static vision accepted by the Aristotelian orthodoxy. He observed the phases of Venus and the rings of Saturn, without identifying them as such; he also interpreted correctly that the sunspots are real features on the surface of the sun. In these and other discoveries, Galileo became immersed in major controversies that almost cost him his life when he faced the Roman Inquisition (censured in 1616 and condemned in 1633). One of these disputes, limited to the academic arena and not resolved until the 20th century, involved the German astronomer Simon Marius (the Latin version of the German name Simon Mayr or Mayer), who claimed co-discovery of Jupiter’s satellites and was attacked roundly by Galileo as a result. The alleged plagiarism, accepted for 300 years, was disproved decades ago, although references to it can still be found in some texts. Let’s look at the sequence of events:
Simon Marius was born in 1570, or probably in 1573, near Nuremberg. He studied astronomy in Prague with the famous Tycho Brahe and Johannes Kepler. He became Brahe’s assistant for a few months, before his death in 1601. For three years until 1605 he studied medicine in Padua. It was in Padua that he may have come into contact with Galileo for the first time, as he lived there from 1592 to 1610, his annus mirabilis, where Galileo was teaching mechanics, geometry and astronomy.
In July 1605 Marius was back in Germany, where he once more took up the position of mathematician in the court of the Margrave of Ansbach, George Frederick. However, one of his students, Baldassarre Capra, entered into conflict on two occasions with Galileo, and even accused him of plagiarism in 1607 with respect to the invention of the military compass. It seems that Galileo thought (without any proof) that the hand of Marius was behind this claim, though the case ended up won by the astronomer from Pisa.
In 1608 Marius had a telescope in his hands for the first time, but his sky observations began in the summer of 1609 (as he himself explained in 1614), thanks to the patronage of Johann Fuchs. In the winter of that year he pointed his telescope toward Jupiter. At that point the controversy begins. It has been heightened and obscured because Marius and Galileo used different calendars and belonged to two opposed worlds. The Catholic countries had already accepted the Gregorian reform, while paradoxically Protestant Germany continued to be anchored to the Julian calendar, which was 10 days behind the real dates. The calendar had been reformed in 1582 and was adopted immediately in Spain and Italy. The German territories outside the dominion of the Hapsburg dynasty would not adopt it until 1700.
According to Marius’ version of events published in 1614 in “Mundus Iovialis” (its 400th anniversary falls this year) he discovered the presence of various uncatalogued “stars” around Jupiter early in December 1609. However on 29th of that month he already suspected that they could actually be orbiting the planet and began to measure their positions. This date corresponded to January 8, 1610 in the Gregorian calendar. The night before, in Italy, Galileo had already discovered three satellites of Jupiter. Marius made methodical observations until January 12 in the Julian calendar, or January 22 in the Gregorian calendar. By that date he believed there were four satellites, and accepted this result as definitive at the end of February or the start of March (once more in the Julian calendar, and according to his version of 1614).
Galileo, on the other hand, understood on January 11 that the “stars” orbited around Jupiter (this was after Marius has suspected that fact, if the version in “Mundus Iovialis” is accepted). Two days later he observed the fourth satellite, before Marius did. In March, Sidereus Nuncius” was published in Venice. At the end of the year he Galileo discovered the phases of Venus, similar to the lunar ones, and notified Kepler of this by letter by means of a curious anagram, and also to Castelli and Clavio, to ensure his claims to priority, although he kept the information unpublished until years later.
Kepler, reacting to “Sidereus Nuncius”, published “Dissertatio cum Nuncio Sidereo” and “Narratio de Observatis a se quatuor Jovis satellitibus erronibus”, and did not mention Marius’s investigations at all. However, in 1611 Kepler published “Dioptrice”, including a fragment of a letter written by Marius to Odentius, a reader in mathematics at the university of Altdorf and friend of both. This fragment makes clear that at least before December 30, 1610, the date of the original letter, Marius knew the phases of Venus and was making observations of Jupiter and compiling tables to predict the positions of its four satellites.
In 1612 Marius described the Andromeda nebula (M31, the closest galaxy) and publicly mentioned for the first time his observations of Jupiter and its satellites in the pamphlet “Frankischer Kalender oder Practica”. A year later, in October 1613, Marius met Kepler, who suggested that the names for the four objects could be the four lovers of the god Zeus, the Greek equivalent of Jupiter: Io, Europa, Ganymede and Callisto (from the closest to the most distant).
Finally, Marius published his observations in “Mundus Iovialis” in 1614; and although he gave credit to Galileo, he also claimed co-discovery. The text included precise astronomical tables to predict the positions of the four satellites at any time (something that Galileo did not provide). He concluded that the orbits are inclined to the ecliptic, a statement that makes clear that Marius obtained very precise observations. In addition, the book proposes various sets of names, and among them includes Kepler’s idea. However, it would be Galileo’s names that were to remain: Roman numerals, with Jupiter I being the closest (Io) and Jupiter IV the most distant (Callisto). It was not until 1847 that John Frederick William Herschel (son of the discoverer of Uranus) would propose the use of individual names taken from Greek and Roman mythology for the multiple satellites of the planet Saturn, following in the wake of Kepler and Marius. It is starting at that time when the current names would begin to be used, although Galileo’s numerals would also continue to be valid.
Galileo’s counter-attack had to wait, as he was focused on his fight with the ecclesiastical authority in Rome and the obsolete image of the world it supported. It was not until 1623, with the publication of “Il Saggiatore” that Galileo unleashed a destructive attack against the reputation of Marius. He rejected the truth of his observations and claimed that the orbits of the four satellites are parallel to the ecliptic (contradicting his own observations and diagrams made two years earlier).
A re-analysis of the observations of the two men leads to the conclusion that Marius was probably honest in his data, although he perhaps did not understand the importance of his discovery in 1610. First, there is the fact that positions of the satellites published by Galileo are relative to the angular size of Jupiter, which he never published. The tables calculated by Marius included these data from Galileo. Given that the results (angular radius of the orbits and of the satellites) are better than those of Galileo, he had to have collected his own observations. Thus both Galileo and subsequent generations of astronomers and historians were unjust with the role he played in the discovery of the satellites.
The irony of this story is that the moons of Jupiter are sufficiently bright to be seen with the naked eye, without the need for a telescope. Ganymede or Jupiter III (the Galilean name) is the biggest (bigger than the Moon or Mercury) and is notably bright, reaching a magnitude of 5 (in comparison, the weakest visible stars on a dark night have a magnitude of 6). This in principle means they can be identified without the aid of a telescope and they could have been discovered in antiquity. But it is Galileo Galilei who left us the first proof of their existence.
What role does the writer Miguel de Cervantes play in this equation? Surprisingly, a lot. His short story “La gitanilla” (“The little gypsie”), belonging to the “Novelas Ejemplares” (“Exemplary Novels”) contains a poem that includes the following lines:
Junto a la casa del Sol
va Júpiter; que no hay cosa
difícil a la privanza
fundada en prudentes obras.
Va la Luna en las mejillas
de una y otra humana diosa;
Venus casta, en la belleza
de las que este cielo forman.
cruzan, van, vuelven y tornan
por el cinto tachonado
de esta esfera milagrosa.
The poem praises the virtues of Queen Margaret of Austria, the wife of Philip III. Cervantes’s scientific culture is evident not only because of the description of the planets and the Sun, assumed at that time by most intellectuals that they revolved around the Earth, according to the geocentric theory. The most remarkable thing is that Cervantes refers to the Jupiter’s satellites shortly after they were discovered, given that the four final verses have an explicit meaning: the words “cruzan, van, vuelven y tornan” (“they cross, go, come back and do it again”) leaves little room for one’s imagination, and would refer to a relatively concise description of orbiting around Jupiter; while the last two verses, “por el cinto tachonado / de esta esfera milagrosa” (“by the gilded belt / of this miraculous sphere”) refers to the Ecliptic, the imaginary circle about which the planets move, and apparently the Sun, and the celestial sphere. Hence, it is written, from an astronomical perspective, and not only from a mythological one.
The dating of the text is relatively simple: it is was published in 1613, the dedication signed in July; the permission by the censure is dated July 2, 1612, and it is was approved seven days later. Kepler’s proposal to Marius about the names of the satellites was made considerably later, in October 1613, according to “Mundus Iovialis”, which appeared in 1614. Therefore, the name suggested by Cervantes clearly predates the suggestion made by the two German astronomers.
Most importantly, it shows signs of Cervantes’s scientific culture and about the dissemination of Galileo’s important discoveries. The poem speaks of a special mass for a royal birth, though it does not specify which was the one in question. Queen Margaret of Austria bore eight children between 1601 and 1611, but the context of the poem appears to suggest that it refers to the last, Alfonso of Austria, who was born and died on September 22, 1611. It is generally assumed, however, that it refers to the birth of the future Philip IV, which occurred on 8 April 1605. If that was the case, then “La Gitanilla” had to have been written between that date and June 1613. From the poem, however, we can assume that it is later than 1610, given that the heroine, Preciosa, is abducted in 1595, and she is 15 years old when the story takes place, and it would be very unusual for Cervantes to have projected the story into the future. It is possible, however, that the romance predated or was subsequent to the novel itself, and that it was included in the text before it went to print. In any event, it is important to bear in mind that “Sidereus Nuncius” was published in March 1610.
It is very unlikely that either Kepler or Marius had access to Cervantes’s “Novelas Ejemplares”. It is possible, though it would be very difficult to prove, that a reader who had enjoyed the work might have mentioned the name Cervantes gave, of little Ganymedes (which is generic name for the four satellites), to Kepler. But it is more plausible that the author of “Don Quixote” might imagine a very fitting name for the small cluster of followers around the largest planet in the Solar System, based on Greek mythology (a rule which has been kept intact until recent times) and that it was exactly the same name suggested by Kepler. Hence, Cervantes would not only the first person to write a novel – and an extraordinary one – in Spanish. Through his poetry, which was not always highly regarded, he would also have given a name to these four objects, satellites that have helped to construct the picture of the world as we know it today.
Finally, it is worth considering that perhaps Cervantes was not the only early seventeenth century Spanish author who refers to aspects of this scientific revolution. It would be interesting to analyze how many astronomic references are can be found in the literature of the second part of the Spanish Golden Age or “Siglo de Oro”. If the number is significant, then it would mean that Spain, at that time, was not as isolated from the breakthroughs being made in human knowledge as one might think. It would certainly be an interesting area for research.
David Barrado Navascués
European Space Astronomy Center (ESAC, Madrid)