This discovery (which became Kepler’s second law of orbital motion) led to the realization of what became Kepler’s first law: that the planets move in an ellipse (a squashed circle) with the Sun at one focus point, offset from the center. For all these triangles to have the same area, the planet must move more quickly when it is near the Sun, but more slowly when it is farthest from the Sun. If you draw a triangle out from the Sun to a planet’s position at one point in time and its position at a fixed time later-say, 5 hours, or 2 days-the area of that triangle is always the same, anywhere in the orbit. For many years, he struggled to make Brahe’s observations of the motions of Mars match up with a circular orbit.Įventually, however, Kepler noticed that an imaginary line drawn from a planet to the Sun swept out an equal area of space in equal times, regardless of where the planet was in its orbit. Like many philosophers of his era, Kepler had a mystical belief that the circle was the Universe’s perfect shape, and that as a manifestation of Divine order, the planets’ orbits must be circular. Italian scientist Giordano Bruno was burned at the stake for teaching, among other heretical ideas, Copernicus’ heliocentric view of the Universe. The theory gathered few followers, and for a time, some of those who did give credence to the idea faced charges of heresy.

Afraid of criticism (some scholars think Copernicus was more concerned about scientific shortcomings of his theories than he was about the Church’s disapproval), he did not publish his theory until 1543, shortly before his death. In 1515, a Polish priest named Nicolaus Copernicus proposed that the Earth was a planet like Venus or Saturn, and that all planets circled the Sun.

Despite that, it was a priest who brought back the idea that the Earth moves around the Sun. A geocentric worldview became engrained in Christian theology, making it a doctrine of religion as much as natural philosophy. For Aristotle, this meant that the Earth had to be stationary, and the planets, the Sun, and the fixed dome of stars rotated around Earth.įor nearly 1,000 years, Aristotle’s view of a stationary Earth at the center of a revolving universe dominated natural philosophy, the name that scholars of the time used for studies of the physical world. He saw no sign that the Earth was in motion: no perpetual wind blew over the surface of the Earth, and a ball thrown straight up into the air doesn’t land behind the thrower, as Aristotle assumed it would if the Earth were moving. One camp thought that the planets orbited around the Sun, but Aristotle, whose ideas prevailed, believed that the planets and the Sun orbited Earth. The ancient Greek philosophers, whose ideas shaped the worldview of Western Civilization leading up to the Scientific Revolution in the sixteenth century, had conflicting theories about why the planets moved across the sky. The world has scarcely become known as round and complete in itself when it was asked to waive the tremendous privilege of being the center of the universe.” -Johann Wolfgang von Goethe “Of all discoveries and opinions, none may have exerted a greater effect on the human spirit than the doctrine of Copernicus. “We revolve around the Sun like any other planet.” -Nicolaus Copernicus

Isaac newton discovered gravity