Galileo Galilei was an Italian scientist who lived from 1564 to 1642 and revolutionized our understanding of the universe. Using a telescope he built himself, Galileo discovered four moons orbiting Jupiter, showing that not everything in space circles Earth. He observed mountains on the Moon, spots on the Sun, and the phases of Venus. These discoveries supported the idea that Earth orbits the Sun, not the other way around.

This got Galileo into serious trouble. The Catholic Church at the time taught that Earth sat at the center of everything. When Galileo argued otherwise, church leaders forced him to recant his views and placed him under house arrest for the rest of his life. Yet he never stopped thinking and writing about science.

Galileo also transformed physics. By carefully timing balls rolling down ramps, he showed that, without air resistance, objects fall at the same rate regardless of their weight, contradicting what many people had believed for centuries. He helped show that experiments and observations matter more than ancient assumptions.

Today, scientists consider Galileo the father of modern science because he insisted on testing ideas rather than just accepting them.