Straddling the bounds of science and religion, Newton wondered who set the planets in motion. Astrophysics reveals the answer.
Perhaps the greatest leaps in all of science history occurred during the 17th century. At the dawn of the century, heliocentrism was just an alternative idea: one that fit the data more poorly than the leading geocentric model that had held sway for over 1000 years. The laws governing the motions of objects on Earth, what we now know as classical mechanics, were largely unknown, and the phenomenon of gravitation was not understood. The telescope had not yet been invented, and naked-eye observations were the still the best tools humanity had for investigating the cosmos.
By the end of the century, everything was different. The planets were at last known to orbit the Sun in ellipses, with the outer planets moving at speeds in proportion to their distance from the Sun. Planets had their own systems of moons, Saturn had rings, Venus exhibited phases, and the laws of motion and gravitation were shown to apply to all known objects on Earth and in the heavens above. This culminated in the work of Isaac Newton, who invented calculus, codified the laws of motion, and developed the universal law of gravitation. Yet Newton…
