Jupiter
Jupiter is the fourth brightest object in the sky (after the Sun, the Moon
and Venus; at some times Mars is also brighter). It has been known since
prehistoric times. Galileo's discovery, in 1610, of Jupiter's four large
moons Io, Europa, Ganymede and Callisto (now known as the Galilean moons)
was the first discovery of a center of motion not apparently centered on
the Earth. It was a major point in favor of Copernicus's heliocentric
theory of the motions of the planets; Galileo's outspoken support of the
Copernican theory got him arrested by the Inquisition. He was
forced to recant his beliefs and was imprisoned for the rest of his life.