Operations of the geometric and military compass, 1606

The Galileo affair was an early 17th century political, religious, and scientific controversy regarding the astronomer Galileo Galilei's defence of heliocentrism, the idea that the Earth revolves around the Sun. It pitted supporters and opponents of Galileo within both the Catholic Church and academia against each other through two phases: an interrogation and condemnation of Galileo's ideas by a panel of the Roman Inquisition in 1616, and a second trial in 1632 which led to Galileo's house arrest and a ban on his books. In 1610, Galileo published his Sidereus Nuncius (Starry Messenger) describing the observations that he had made with his new, much stronger telescope, amongst them the Galilean moons of Jupiter. With these observations and additional observations that followed, such as the phases of Venus, he promoted the heliocentric theory of Nicolaus Copernicus published in De revolutionibus orbium coelestium in 1543. Galileo's opinions were met with opposition within the Catholic Church, and in 1616 the Inquisition declared heliocentrism to be both scientifically indefensible and heretical.