Ganymede (moon) common use until the mid-20th century. In much of the earlier astronomical literature, Ganymede is referred to instead by its Roman numeral designation, (a system introduced by Galileo), in other words "the third satellite of Jupiter". Following the discovery of moons of Saturn, a naming system based on that of Kepler and Marius was used for Jupiter's moons. Ganymede is the only Galilean moon of Jupiter named after a male figure—like Io, Europa, and Callisto, he was a lover of Zeus. Ganymede orbits Jupiter at a distance of 1,070,400 km, third among the Galilean satellites, and completes a revolution every
Orbit of the Moon rearward loops in the Moon's solar orbit. Considering the Earth–Moon system as a binary planet, its centre of gravity is within Earth, about or 72.6% of the Earth's radius from the centre of the Earth. This centre of gravity remains on the line between the centres of the Earth and Moon as the Earth completes its diurnal rotation. The path of the Earth–Moon system in its solar orbit is defined as the movement of this mutual centre of gravity around the sun. Consequently, Earth's centre veers inside and outside the solar orbital path during each synodic month as the Moon