Galileo Turns the Telescope to the Heavens
Galileo built a telescope in 1609, pointed it upward, and published what he saw the following March. The instrument was not his invention. Spectacle-makers in the Netherlands had produced one the previous year, and Galileo heard a description, worked out the principle, and ground better lenses than anyone else could, reaching about twenty times magnification when the Dutch instruments managed three. He sold the design to Venice as a naval instrument first. The Sidereus Nuncius of March 1610 is twenty-four pages and it dismantled the physics of the previous two thousand years. The Moon has mountains and craters, so it is not a perfect celestial sphere but a body like the Earth. The Milky Way resolves into individual stars, so there are far more stars than anyone had counted. Jupiter has four moons going round it, which means not everything orbits the Earth. He named them the Medicean stars and got a court appointment in Florence for it. Venus turned out to show a full set of phases, which is impossible in Ptolemy's arrangement and required at minimum the model of Tycho Brahe. None of this proved that the Earth moves, and Galileo argued as though it did. He was warned in 1616, published the Dialogue in 1632 putting the pope's argument in the mouth of a character called Simplicio, and was tried and confined to his house for the remaining nine years of his life. The verdict was formally regretted by the church in 1992. The instrument itself changed what counted as evidence. Before 1610 astronomy was argument from geometry and the naked eye, and afterwards it was argument from an apparatus that most people could not check for themselves and had to be persuaded to trust.
- Year: 1609 CE
- Category: Scientific
