When were the Galilean moons of Jupiter discovered?

Answer 1

The four Galilean moons, were discovered in 1610 by Galileo Galilei who was the first to publish his telescopic observations of the planet and were the first objects found to orbit a body that was neither Earth nor the Sun

Answer 2

The first claimed observation of one of Jupiter's moons is that of the Chinese astronomer Gan De around 364 BC. In fact it is not all that difficult to see one or more of the largest 4 moons. The trick is not to be "blinded" by Jupiter's brightness. To to that place yourself where something rather small blocks just Jupiter on some very dark night (I used a power line strung between poles a tree twig would work as well).

On 7 January 1610 Galileo observed with his telescope what he described at the time as "three fixed stars, totally invisible by their smallness," all close to Jupiter, and lying on a straight line through it. Observations on subsequent nights showed that the positions of these "stars" relative to Jupiter were changing in a way that would have been inexplicable if they had really been fixed stars. On 10 January Galileo noted that one of them had disappeared, an observation which he attributed to its being hidden behind Jupiter. Within a few days he concluded that they were orbiting Jupiter: He had discovered three of Jupiter's four largest satellites (moons): Io, Europa, and Callisto. He discovered the fourth, Ganymede, on 13 January. No additional satellites were discovered until E.E. Barnard observed Amalthea in 1892. With the aid of telescopic Photography, further discoveries followed quickly over the course of the twentieth century. Himalia was discovered in 1904, Elara in 1905, Pasiphaë in 1908, Sinope in 1914, Lysithea and Carme in 1938, Ananke in 1951, and Leda in 1974. By the time Voyager space probes reached Jupiter around 1979, 13 moons had been discovered, while Themisto was observed in 1975, but due to insufficient initial observation data, it was lost until 2000. The Voyager missions discovered an additional three inner moons in 1979: Metis, Adrastea, and Thebe. For two decades no additional moons were discovered; but between October 1999 and February 2003, researchers using sensitive ground-based detectors found another 32 moons, most of which were discovered by a team led by Scott S. Sheppard and David C. Jewitt. These are tiny moons, in long, eccentric, generally retrograde orbits, and average of 3 km (1.9 mi) in diameter, with the largest being just 9 km (5.6 mi) across. All of these moons are thought to be captured asteroidal or perhaps cometary bodies, possibly fragmented into several pieces, but very little is actually known about them. A number of 14 additional moons were discovered since then, but not yet confirmed, bringing the total number of observed moons of Jupiter at 63. As of 2008, this is the most of any planet in the Solar System, but additional undiscovered, tiny moons may exist. Jupiter has 63 confirmed moons, giving it the largest retinue of moons with "reasonably secure" orbits of any planet in the Solar System. The most massive of them, the four Galilean moons, were discovered in 1610 by Galileo Galilei and were the first objects found to orbit a body that was neither Earth nor the Sun. From the end of the 19th century, dozens of much smaller Jovian moons have been discovered and have received the names of lovers, conquests, or daughters of the Roman god Jupiter, or his Greek equivalent, Zeus. Eight of Jupiter's moons are regular satellites, with prograde and nearly circular orbits that are not greatly inclined with respect to Jupiter's equatorial plane. The Galilean satellites are spheroidal in shape, and so would be considered dwarf planets if they were in direct orbit about the Sun. The other four regular satellites are much smaller and closer to Jupiter; these serve as sources of the dust that makes up Jupiter's rings. Jupiter's other 54 or 55 moons are tiny irregular satellites, whose prograde and retrograde orbits are much farther from Jupiter and have high inclinations and eccentricities. These moons were likely captured by Jupiter from solar orbits. There are 13 recently-discovered irregular satellites that have not yet been named, plus a 14th whose orbit has not yet been established