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Simon Marius (Latinized from German Simon Mayr; January 20, 1573 – January 5, 1625) was a German astronomer. He was born in Gunzenhausen, near Nuremberg, but he spent most of his life in the city of Ansbach.

Simon Marius
Houghton GC6 M4552 614m - Simon Marius - cropped.jpg
Simon Marius
Born January 20, 1573(1573-01-20)
Gunzenhausen, Principality of Ansbach
Died January 5, 1625(1625-01-05) (aged 51)
Ansbach, Principality of Ansbach
Residence Ansbach
Nationality German
Fields Astronomy
Known for Jupiter, Andromeda Galaxy

In 1614 Marius published his work Mundus Iovialis describing the planet Jupiter and its moons. Here he claimed to have discovered the planet's four major moons some days before Galileo Galilei. This led to a dispute with Galileo, who in Il Saggiatore in 1623 accused Marius of plagiarism. 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 started keeping notes one day later than Galileo, when Marius's date in the Julian calendar is increased by 10 days to convert to the Gregorian calendar used by Galileo.[1]

Regardless of priority, the mythological names by which these satellites are known today (Io, Europa, Ganymede and Callisto) are those given them by Marius:[2]

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 Arab astronomers of the Middle Ages.[citation needed] 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,[3] like "a candle shining through horn".[4]
  • That he detected the spurious disks of stars created by his telescope.[5]
  • That, from his observations of the Jovian moons he derived better periods of revolution and other orbital elements for them than did Galileo.[6]
  • 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."[7]

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.[8] He also concluded from his observations of the Jovian moons that they must orbit Jupiter while Jupiter orbits the Sun.[9] 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.[10]


  • 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. ^ 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. doi:10.1177/0021828615585493. 
  2. ^ Marius/Schlör, Mundus Iovialis, p. 78 f. (with misprint In for Io)
  3. ^ 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.
  4. ^ Watson, Fred, Stargazer: The Life and Times of the Telescope, Da Capo Press, 2005, pg. 86.
  5. ^ Dreyer, JLE,"The Tercentenary of the Telescope",Nature,vol. 82 (December 16, 1909), pp. 190–191
  6. ^ Pannekoek, Anton, A History of Astronomy, Interscience Publishers, 1989, pg. 231.
  7. ^ Waldrop, M. Mitchell,"Supernova 1987 A: Facts and Fancies",Science,New Series, Vol. 239, No. 4839 (Jan. 29, 1988), pp. 460–462
  8. ^ Marius/Schlör, Mundus Iovialis, pp. 46–49.
  9. ^ Marius, Simon (tr. by A.O. Prickard), "The Mundus Jovialis of Simon Marius", The Observatory (astronomy), vol. 39, 1916, pg. 404, 408, 409
  10. ^ Marius/Schlör, Mundus Iovialis, pp. 46–49.

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