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Simon Marius (Latinized from German Simon Mayr; January 20, 1573 – January 5, 1625[1]) was a German astronomer. He was born in Gunzenhausen, near Nuremberg, but he spent most of his life in the city of Ansbach. He is most noted for making the first observations of the four largest moons of Jupiter, before Galileo himself, and his publication of his discovery led to charges of plagiarism. He is also known for the first European observation of the Andromeda Galaxy.

Simon Marius
Simon Marius.jpg
Born(1573-01-20)January 20, 1573
DiedJanuary 5, 1625(1625-01-05) (aged 51)
Ansbach, Principality of Ansbach
Known forJupiter, Andromeda Galaxy
Scientific career


Early lifeEdit

Marius was the son of Reichart Mayr, a mayor of Gunzenhausen.[2] On the recommendation of George Frederick, Margrave of Brandenburg-Ansbach, he was admitted to the Margrave's Academy in Heilsbronn in 1586, where he studied until 1601.[3] During this time, he published observations about a comet as well as astronomical tables, which gave him a reputation as a good astronomer and mathematician, and the Margrave appointed him as his official mathematician.[2] Marius wanted to attend the University of Königsberg, but was unable to get a scholarship.[3] However, the Margrave wrote a letter of recommendation on May 22, 1601, so that Marius could study in Prague under Tycho Brahe, which he did for several months,[2] although he may actually have worked directly with David Fabricius instead of Brahe himself.[3]

By September 1601, Marius had already left Prague and he arrived in Padua in December 1601 to study medicine at the University of Padua.[1] During this time, he tutored other students in astronomy, including one Baldassarre Capra, with whom he wrote a book on a new star (actually Kepler's Supernova) they observed in 1604.[2] Capra had a dispute with Galileo Galilei (both of them learned fencing from Capra's father[4]) on the invention of the proportional compass and Marius took his student's side in the argument.[3] Marius left the school in July 1605, returning to Ansbach to become the mathematician and physician to the new Margraves, Christian and Joachim Ernst.[2]

In 1606, Marius married Felicitas Lauer, the daughter of his publisher, in Nuremberg, and in 1609 he published the first German translations of Euclid's Elements. That year, he also built his own telescope and in November made observations of the Galilean moons, slightly before Galileo did himself, which became the source of a major dispute between the two.[2]

Dispute with GalileoEdit

Capra published another book in 1607 which he actually plagiarised from Galileo, and Marius was implicated in the act due to his prior association with Capra, even though this was after Marius had left Padua. Galileo certainly was under that impression, as he referred to his "old adversary" (without explicitly naming Marius) as a "poisonous reptile", and an "enemy of all mankind".[2]

In 1614, Marius published his work Mundus Iovialis describing the planet Jupiter and its moons (he previously had published the discovery in 1611 in a local almanac[5]). Here he claimed to have discovered the planet's four major moons about a month before Galileo, who was naturally incensed. In The Assayer in 1623, he accused Marius of plagiarism.[2]

Because of Galileo's stature in the scientific community, for nearly 300 years, Marius's reputation was tainted by Galileo's accusations. However, a jury in the Netherlands in 1903 examined the evidence extensively and ruled in favor of Marius's independent discoveries, with results published by Bosscha in 1907. Apparently Marius discovered the moons independently, but did not start keeping notes until December 29, 1609. Marius used the Julian calendar, and that date is equivalent to January 8, 1610, in the Gregorian one used by Galileo, one day after Galileo's letter in which he first described the moons.[5]

Regardless of priority, the mythological names by which these satellites are known today (Io, Europa, Ganymede and Callisto) are those given them by Marius:[6]

Io, Europa, Ganimedes puer, atque Calisto
lascivo nimium perplacuere Iovi.

Io, Europa, the boy Ganymede, and Callisto
greatly pleased lustful Jupiter.


Simon Marius also observed the Andromeda "nebula", which had also been known to Persian astronomers of the Middle Ages.[7]

Discussion of Marius's work is scarce, but what exists tends to note his skill as an observer, including:

  • That in 1612 he measured the diameter of the Andromeda nebula and discerned it as having a dull, pale light which increased in brightness toward its center,[8] like "a candle shining through horn".[9]
  • That he detected spurious disks of stars created by his telescope.[10]
  • That, from his observations of the Galilean moons he derived better periods of revolution and other orbital elements for them than did Galileo.[11]
  • That he observed the location of Tycho Brahe's supernova of 1572 and found a star there which he estimated to be "somewhat dimmer than Jupiter's third moon".[12]

Marius drew conclusions about the structure of the universe from his observations of the Jovian moons and the stellar disks. The stellar disks he observed were spurious (likely the Airy disk caused by diffraction, as stars are too distant for their physical disks to be detected telescopically), but Marius interpreted them to be physical disks, like the planetary disks visible through a telescope. He concluded that since he could see stellar disks, the stars could not be as distant as was required in the Copernican world system, and he said that the appearance of the stars as seen through a telescope actually argued against Copernicus.[13] He also concluded from his observations of the Galilean moons that they must orbit Jupiter while Jupiter orbits the Sun.[14] Therefore, Marius concluded that the geocentric Tychonic system, in which the planets circle the Sun while the Sun circles the Earth, must be the correct world system, or model of the universe.[15]


  • Mundus Iovialis anno MDCIX Detectus Ope Perspicilli Belgici (Die Welt des Jupiter, 1609 mit dem flämischen Teleskop entdeckt; Lateinisches Faksimile und deutsche Übersetzung; Hrsg. und bearb. von Joachim Schlör. Naturwiss. begleitet und mit einem Nachw. vers. von Alois Wilder), 1614
  • Zinner, E., "Zur Ehrenrettung des Simon Marius", in: Vierteljahresschrift der Astronomischen Gesellschaft, 77. Jahrgang, 1. Heft, Leipzig 1942
  • Bosscha, J., "Simon Marius. Réhabilitation d´un astronome calomnié", in: Archives Nederlandaises des Sciences Exactes et Naturelles, Ser. II, T. XII, pp. 258–307, 490–528, La Haye, 1907


  1. ^ a b Rosen, Edward (2008). "Mayr (Marius), Simon". Complete Dictionary of Scientific Biography. Charles Scribner's Sons. Retrieved January 2, 2019 – via
  2. ^ a b c d e f g h O'Connor, John J.; Robertson, Edmund F., "Simon Marius", MacTutor History of Mathematics archive, University of St Andrews.
  3. ^ a b c d Folkerts, Menso (1990), "Marius (Mayr), Simon", Neue Deutsche Biographie (NDB) (in German), 16, Berlin: Duncker & Humblot, pp. 217–218; (full text online)
  4. ^ Clelia Pighetti, Il vuoto e la quiete. Scienza e mistica nel '600: Elena Cornaro e Carlo Rinaldini, Milano, Franco Angeli, 2005, p. 27. (in Italian)
  5. ^ a b Pasachoff, Jay M. (May 2015). "Simon Marius's Mundus Iovialis: 400th Anniversary in Galileo's Shadow". Journal for the History of Astronomy. 46 (2): 218–234. Bibcode:2015JHA....46..218P. doi:10.1177/0021828615585493.
  6. ^ Marius/Schlör, Mundus Iovialis, p. 78 f. (with misprint In for Io)
  7. ^ Hafez, Ihsan (2010). "Abd al-Rahman al-Sufi and his book of the fixed stars: a journey of re-discovery". PhD Thesis, James Cook University. Retrieved June 23, 2016.
  8. ^ Bond, George P., "An Account of the Nebula in Andromeda", Memoirs of the American Academy of Arts and Sciences, New Series, volume 3, 1848 pp. 75–76.
  9. ^ Watson, Fred, Stargazer: The Life and Times of the Telescope, Da Capo Press, 2005, pg. 86.
  10. ^ Dreyer, JLE, "The Tercentenary of the Telescope", Nature, vol. 82 (December 16, 1909), pp. 190–191
  11. ^ Pannekoek, Anton, A History of Astronomy, Interscience Publishers, 1989, pg. 231.
  12. ^ Waldrop, M. Mitchell,"Supernova 1987 A: Facts and Fancies",Science, New Series, Vol. 239, No. 4839 (January 29, 1988), pp. 460–462
  13. ^ Marius/Schlör, Mundus Iovialis, pp. 46–49.
  14. ^ Marius, Simon (tr. by A.O. Prickard), "The Mundus Jovialis of Simon Marius", The Observatory (astronomy), vol. 39, 1916, pp. 404, 408, 409
  15. ^ Marius/Schlör, Mundus Iovialis, pp. 46–49.

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