Galileo Galilei (1564-1642)

Galileo was the first European to make systematic observations of the heavens by means of the telescope. Don't get confused. he DID NOT invent the telescope. The telescope had previously been invented to look at far distances on Earth (particularly for war purposes). By using the telescope Galileo seemed to destroy yet another aspect of the traditional thought that the universe was composed of material substance similar to that of the Earth (which indeed it wasn't). These new findings were published in his book, The Starry Messenger. In the book Galileo also revealed his advocacy to the heliocentric theory made by Copernicus. Galileo was a friend of the Pope and so he was commissioned to write a book which content focused on the debate between the Copernicus theory and the Ptolemaic theory. Though, in the debate (in the book) the Copernican  theory was greatly defended and it was made obvious who won the argument. Galileo was soon after placed upon house arrest. Galileo also made contributions to the problem of motion. He discovered inertia which stated tat an object in motion stays in motion unless acted upon by an outside force.