Galileo's observations revolutionize understanding of planetary motion Through the innovative use of the telescope to study the sky, the Italian scientist Galileo made observations early in the 1600's that supported the theory that the earth is a moving planet. Proposed in the 1500's by the Polish astronomer Nicolaus Copernicus, this revolutionary idea challenged long-held beliefs that the motionless earth is the center of the universe. Click here for information on how to get one of the latest guides to the stars and planets. View from Today