Why Heliocentrism Was Actually Wrong At First - Terence Tao

Tao begins by noting that Copernicus' heliocentric theory was initially less accurate than Ptolemy's geocentric model, which had been refined over a millennium with increasingly complex modifications. While Copernicus proposed that planetary orbits were perfect circles in a simpler model, it was much less accurate than existing theories. Kepler later made the heliocentric model more accurate than Ptolemy's geocentric theory. Kepler initially had a beautiful geometric theory involving the five Platonic solids fitting perfectly between the six known planetary orbits, believing this represented God's mathematical design of the solar system. To test this theory, Kepler needed high-quality observational data, which came from Tycho Brahe, a Danish astronomer who had convinced the Danish government to fund an expensive observatory on an entire island where he spent decades collecting planetary observations. When Kepler analyzed Brahe's data, he was disappointed to find that his elegant Platonic solid theory was off by about 10%, and various adjustments couldn't make it work. After years of brilliant data analysis, Kepler discovered that planetary orbits were actually ellipses rather than circles, which was shocking to him. This led to his first two laws of planetary motion: planets move in ellipses and sweep out equal areas in equal times. Ten years later, after collecting more data, he formulated his third law relating orbital periods to distances from the sun. All three laws were purely empirical discoveries without theoretical explanation, and it took Newton a century later to provide the underlying theory that explained all three laws simultaneously.