Galileo Galilei

Galileo Galilei, a contemporary of Kepler, built a telescope and began fixing its lens on the planets. He made a series of remarkable discoveries: that the moon was not flat and smooth, there were spots on the sun, Jupiter had moons that orbited it, Venus had phases like the moon, which proved that the planet rotated around the sun.

Galileo published his findings but was later put on trial for heresy and put under house arrest for the remainder of his life. He never stopped his research and published several theories until his death in 1642.