Nicolaus Copernicus makes his first recorded astronomical observation. Copernicus is the first scientists to construct a working heliocentric model of the solar system and his work is regarded as the starting point of modern astronomy.
In addition to being an accomplished astronomer, Copernicus is also a mathematician, a diplomat, an economist, an artist, and a translator (among many other things). Although his work isn't immediately and widely accepted, Copernicus' ideas will undermine centuries of assumption and superstition. Indeed, Copernicus' discoveries carry consequences not everyone today fully recognizes.