Today a discovery might have been discovered.
When Galileo built his first telescopes in the early 1600s, he was already a follower of Copernicus’ heliocentric theory (putting the sun at the center of nearby planetary revolutions, and the motion of stars more independently distant). It was as much a belief as anything else, just like the Church’s conviction that all celestial objects revolved around the Earth. Galileo put his favored theory to test, however, and with his extended sight discovered sunspots, phases of Venus, rings of Saturn, moons of Jupiter and, on this day in 1613, chanced upon a mysterious star that moved like a planet would move, though none had been expected in the spot in which he saw it. He was soon thereafter censured by the Church and would spend the next twenty years sparring with it on various issues (like tides and comets) before standing trial for heresy in 1633.
That star was the planet Neptune, which was officially discovered more than 200 years later when British and French mathematicians predicted its position based on studies of the movement of Uranus (which suggested another planet was tugging on it gravitationally). Subsequent computer models confirm that its the same point of light in the sky that Galileo saw. He had to know it wasn’t a star, and he may have shared his discovery with his friends, but we don’t know because his notes were often written in secret code.
Whether a planet, star, or smudge on a telescope lens, it’s a good bet he found what he was looking for.
