Galileo > Siderius Nuncius
The Siderius Nuncius or "Starry Messenger" is a thin pamphlet, very unassuming for the first publication of modern observational astronomy. In this work Galileo presents the astronomical observations he accomplished using a telescope, with which he was able to discern the craters on the moon, the myriad stars of the Milky Way, and the satellites of Jupiter. Few owned the instruments at the time, and even fewer had access to the higher quality telescopes that Galileo used and sold on the side throughout his life. Galileo considered himself a Copernican, and while none of his work proved that the Copernican view of the world was right, it proved beyond doubt that the Aristotelian/Ptolemaic world-view was wrong. He would write his Letter to the Grand Duchess five years later.