Galileo reports telescopic discoveries
Galileo reports telescopic discoveries
Overview
In 1610 Galileo Galilei published Sidereus Nuncius, reporting the first telescopic observations of the heavens: mountains on the Moon, countless unseen stars, the phases that Venus would later display, and four moons orbiting Jupiter. Each observation undermined a piece of the Aristotelian cosmos — celestial bodies were imperfect, and not everything orbited Earth. The discoveries established the telescope as astronomy's essential instrument and gave heliocentrism its first direct observational support.