[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) which they had observed in 1604.

[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.

That year, he also built his own telescope and in November made observations of the Galilean moons, slightly before Galileo did himself; this became the source of a major dispute between the two.

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".

However, a scientific committee in the Netherlands in 1903 examined the evidence extensively and ruled in favor of Marius's independent discoveries, with results published by Johannes Bosscha in 1907.

[6] Regardless of priority, the mythological names by which these satellites are known today (Io, Europa, Ganymede and Callisto) are those given them by Marius:[9]

[16] These findings are contrasting to those of Galileo, who utilized similar telescopic data alternatively to support the Copernican world system.