Simon Marius

• 1. Introduction

  ›

  Simon Marius stared at Jupiter through a telescope he had built himself and saw four small points of light that would define his legacy and haunt his reputation for nearly three centuries. Born on the 10th of January 1573 in Gunzenhausen, near Nuremberg, he spent most of his life in the city of Ansbach. His name is inseparable from a bitter rivalry with Galileo Galilei, charges of plagiarism, and a slow, painstaking rehabilitation that would not begin in earnest until 1903. Yet the names we use today for Jupiter's four largest moons, Io, Europa, Ganymede, and Callisto, are not Galileo's names. They are Marius's. This is the story of an astronomer who gave the solar system some of its most enduring vocabulary, and who paid a heavy price for it.

• 2. From Gunzenhausen to Padua

  ›

  George Frederick, Margrave of Brandenburg-Ansbach, took a direct interest in the young Marius and recommended him for admission to the Margrave's Academy in Heilsbronn in 1586. Marius studied there until 1601, long enough to publish observations of a comet and produce astronomical tables that earned him a reputation as a capable astronomer and mathematician. The Margrave rewarded him with an official appointment as his mathematician. Marius had wanted to enroll at the University of Konigsberg, but no scholarship materialized. The Margrave stepped in again, writing a letter of recommendation dated the 22nd of May 1601 so that Marius could study in Prague under Tycho Brahe. He spent several months there, though it is possible he worked more directly with David Fabricius than with Brahe himself. By September 1601 he was already gone from Prague. He arrived in Padua in December 1601 to study medicine at the University of Padua, and there he began tutoring other students in astronomy. One of those students was a young man named Baldassarre Capra.

• 3. The Capra Entanglement

  ›

  Capra and Marius collaborated on a book about the new star they had both observed in 1604, the object now known as Kepler's Supernova. That collaboration would mark Marius in ways he could not have anticipated. Capra was already in conflict with Galileo Galilei over the invention of the proportional compass. Both Capra and Galileo had, notably, learned fencing from Capra's father. Marius took his student's side in the dispute. He left Padua in July 1605, returning to Ansbach to serve as mathematician and physician to the new Margraves, Christian and Joachim Ernst. Two years later, in 1607, Capra published a book that plagiarized directly from Galileo. Marius had already left Padua, but his prior association with Capra was enough for Galileo to link them. Galileo referred to an "old adversary", without naming Marius explicitly, as a "poisonous reptile" and an "enemy of all mankind". The accusation cast a shadow that would follow Marius for the rest of his life and well beyond it.

• 4. Jupiter's Moons and the Priority Dispute

  ›

  In 1609, Marius built his own telescope and began observing the four large moons of Jupiter at roughly the same time Galileo did. He first noted his discovery on the 29th of December 1609 according to the Julian calendar. That date, when converted to the Gregorian calendar that Galileo used, equals the 8th of January 1610, one day after Galileo's letter in which he first described the moons. Marius announced his discovery in a local almanac in 1611, then published a full account in 1614 in his book Mundus Iovialis, the World of Jupiter. He claimed in that work to have found the moons about a month before Galileo. Galileo was enraged. In The Assayer, published in 1623, he formally accused Marius of plagiarism. Because of Galileo's standing in the scientific world, the accusation stuck. For nearly 300 years, Marius's reputation bore the stain of it. A scientific committee in the Netherlands took up the question in 1903, examined the evidence at length, and ruled in Marius's favor: he had made his observations independently. Johannes Bosscha published those findings in 1907, and the rehabilitation of Simon Marius was officially, if belatedly, underway.

• 5. Readings of the Sky

  ›

  Beyond Jupiter, Marius turned his telescope to the Andromeda nebula, which Persian Muslim astronomers of the Middle Ages had already known. In 1612, he measured the diameter of that nebula and described its light as dull and pale, brightening toward the center like, in his own words, "a candle shining through horn". That phrase stands as one of the more striking observational descriptions to survive from early telescopic astronomy. Marius also detected what he took to be physical disks on stars, and he noted the orbital periods of the Galilean moons with greater precision than Galileo managed. He observed the location of Tycho Brahe's supernova of 1572 and estimated a star he found there to be somewhat dimmer than Jupiter's third moon. In 1606, the year after he left Padua, he had married Felicitas Lauer, born in 1590, the daughter of his own publisher. And in 1609, the same year he trained his telescope on Jupiter, he published the first German translations of Euclid's Elements.

• 6. A Universe Through a Flawed Lens

  ›

  The stellar disks Marius observed were not real. They were almost certainly the Airy disk, an artifact of diffraction that makes point sources of light appear to have measurable size when seen through a telescope. Stars are too distant for their physical disks to be detected optically. Marius, unaware of this, treated what he saw as genuine. He reasoned that if stars had visible disks, they could not be as far away as the Copernican system required. His telescope data, he argued, actually worked against Copernicus. Galileo drew the opposite conclusion from similar observations, using telescopic evidence to support the Copernican heliocentric model. Galileo's commitment to Copernicus, the source notes, arose from that theory's mathematical elegance and his prior investment in it. Marius, by contrast, showed no evident allegiance to any theoretical framework. He reasoned from what he saw. From his observations of the Galilean moons, he concluded they orbited Jupiter while Jupiter orbited the Sun. That evidence pointed him toward the Tychonic system, in which the planets circle the Sun but the Sun itself circles the Earth. The names Io, Europa, Ganymede, and Callisto, which Marius assigned to those moons, outlasted both his theory and his long eclipse from scientific memory.