In the sixteenth century, Nicolaus Copernicus concluded that the planets traveled around the Sun. This was a very controversial idea, because it seemed to contradict the Bible and all the accepted traditions of the time.

In 1610, Galileo Galilei used a new optical instrument -- known today as a telescope -- to look at the night sky. He discovered several points of light close to the planet Jupiter. He assumed they were stars, fixed in the heavens, but their strange alignment intrigued him. The next night he looked again, and saw that they had changed position. The bright points were dancing around Jupiter --- they were not acting like stars at all. Galileo realized he was seeing bodies in orbit around Jupiter. Copernicus was right - the heavens do not revolve around Earth.

Originally, Galileo named Jupiter's four bright moons after his sponsor, the Medici family. Later, the moons were called Io, Europa, Ganymede, and Callisto, after mythical persons who were companions of the god Jupiter. In honor of Galileo, they are now called the Galilean moons.

Acknowledged as first experimental scientist

One of first to use telescope to observe the heavens

First to observe Jupiter's four largest moons, 1610

Observed Saturn, Earth's Moon, and the Sun

Observations supported Copernican heliocentric system

Catholic Church invoked the Inquisition against Galileo in 1616

Sentenced to indefinite imprisonment by the Church until his death

Catholic Church reopened the case in 1979; studied for13 years before acquitting Galileo