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Jupiter Gallery

Rings of Jupiter

Medicea Sidera

Moons of Jupiter:

Medicea Sidera

Medicea Sidera - Io, Europa, Ganymede and Callisto Similar to Cassini and his Sidera Lodoicea, Galileo Galilei (1564-1642) discovered four moons around Jupiter in January 1610:

  1. Io
  2. Europa
  3. Ganymede
  4. Callisto

Galileo GalileiGalileo named this group of moons in honor of Cosimo de’ Medici, Grand Duke of Tuscany. He was trying to secure patronage from the Duke and succeeded using the moons as leverage. Cosimo Sidera means Cosimo's Stars. Simon Marius claimed to have discovered the moons at the same time and published a paper giving the moons the names they are known by today. Luckily we all see through that and give Galileo the credit for discovering them and refer to them collectively as the Galilean Moons.

The discovery of these moons caused quite a controversy at the time because the commonly held belief was that all celestial bodies revolved around the Earth (e.g. Ptolemaic world system). These moons obviously revolved around Jupiter.

Another interesting face is that for every time Ganymede revolves around Jupiter, Europa revolves twice and Io revolves four times. Callisto messes it all up with it's one revolution per 9.4 revolutions of Io.

These moons are the four largest around Jupiter and all but Europa are larger than Earth's moon. See all Jupiter's moons.

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Io Europa Ganymede Callisto