Galileo Galilei was an astronomer and physicist whose genius challenged the geocentric (Earth-centered) view of the universe. He was the first to use a telescope to observe the heavens, discovering sunspots, the phases of Venus, and the four large moons of Jupiter. These observations provided the empirical evidence needed to support Copernicus's heliocentric model. Galileo’s genius also extended to the study of motion; he established the concept of inertia and showed that acceleration due to gravity is constant. His refusal to recant his scientific findings led to his trial by the Inquisition and life under house arrest, making him a lasting symbol of the struggle for scientific freedom. Image of Galileo's telescope designs