Summary
Highlights
Galileo, working in Southern Europe in the early 1600s, was a contemporary of Kepler and corresponded with him. He was the first person known to point a telescope, which was invented in Northern Europe, towards the sky. His observations contradicted many ancient Greek ideas and supported Kepler's laws of planetary motion.
Galileo observed the moon, discovering craters and mountains, proving it was not a 'perfect sphere' as the Greeks believed, but a ball of rock with a landscape similar to Earth's. He also observed Jupiter and its four largest moons (Europa, Io, Ganymede, Callisto), which orbited Jupiter, demonstrating that Earth was not the only center of motion. This observation supported the heliocentric model.
Galileo observed that Venus goes through phases, similar to the Moon. The Ptolemaic (Greek) model predicted different phases than what was observed, indicating a flaw in their model. The Copernican and Keplerian models, however, correctly predicted the phases of Venus, further cementing the heliocentric theory. Galileo's work encouraged a scientific approach, allowing anyone to verify his observations with a telescope.
Beyond astronomy, Galileo also worked on physics, specifically the laws of motion, laying groundwork for what would later be attributed to Newton. Due to his publications and findings, Galileo was placed under house arrest for the remainder of his life, although he continued his studies.
Isaac Newton was born in the same year Galileo died (1642). Newton further developed Galileo's work, especially during his time isolated due to the plague in the 1660s. He established fundamental ideas in physics, astronomy, and mathematics, including the laws of motion, optics, the theory of gravity, and calculus. While Einstein's theories of relativity later modified Newton's laws of gravity, Newton's laws of motion and discoveries in optics, including a telescope design still in use, remain foundational. This period marked a significant advance in modern physics and astronomy, leading to discoveries like new planets and technologies like photography.