When did Galileo Galilei first observe Jupiter's moons?
Galileo Galilei wrote the first letter mentioning Jupiter's moons on the 7th of January 1610. He observed all four moons for the first time on the 13th of January 1610.
Questions about Galilean moons
Short answers, pulled from the story.
Who named the Galilean moons and when was the discovery published?
Simon Marius claimed to have observed the moons in November 1609 with a written record dated the 29th of December 1609. The discovery was announced in Sidereus Nuncius published in Venice in March 1610 less than two months after the initial observations.
Which Galilean moon is the most geologically active object in the Solar System?
Io has over 400 active volcanos making it the most geologically active object in the Solar System. Its surface contains more than 100 mountains some of which are taller than Earth's Mount Everest.
What makes Ganymede unique among natural satellites in the Solar System?
Ganymede is the largest natural satellite in the Solar System at 5262.4 kilometers in diameter. It is the only satellite known to possess a magnetosphere likely created through convection within its liquid iron core.
How did Chinese astronomers observe Jupiter's moons before Galileo?
Chinese astronomical records report that Gan De detected what might have been a moon of Jupiter in 365 BC with the naked eye. A historian claims a small reddish star observed near Jupiter in 364 BCE by Gan De may have been Ganymede.