Nicolaus Copernicus proposed a model of the solar system with the Sun at the center, replacing the Earth-centered model. Johannes Kepler discovered that planets orbit the Sun in ellipses rather than perfect circles, with the Sun located at one focus of the ellipse. Galileo Galilei made important astronomical observations using his telescope that supported Copernicus' sun-centered model of the universe and showed that planets were not points of light but had surfaces like the Moon. Sir Isaac Newton formulated the law of universal gravitation, explaining that gravity causes planets to follow elliptical orbits around the Sun.

1. The Birth of Modern Astronomy Earth Science 1st semester Mr. Riordan