Galileo Galilei is famous for his physics-related and astronomy-related observations. He built his own telescope in 1609 and used it to study the cosmos, eventually concluding that Earth’s solar system is heliocentric. Galileo’s theories on motion were later used as the foundation of Isaac Newton’s work.
Galileo was commissioned by local merchants to build telescopes to spot incoming ships, and he later used the invention to explore the stars. In 1610, he discovered that the moon was round with craters and mountains, Jupiter had its own moons, and Venus had phases. He also observed sunspots. These observations contradicted the prevailing theory supported by Aristotle and the Catholic church that the Earth was the center of the universe, with the heavenly bodies revolving around it. Galileo instead supported the Copernican theory that the sun was the center of the solar system, and the Earth and other planets revolve around it. He was accused of heresy twice during his life for his astronomy beliefs, the second time resulting in house arrest that lasted until his death.
Galileo was credited with conducting an experiment involving dropping two objects from the Leaning Tower of Pisa to prove that objects fall at the same speed regardless of their mass. Although it is unproven that this experiment took place, Galileo is credited with fathering this theory, which later became the basis of Newton’s second law of physics.