Galileo Galilei’s greatest achievement was his significant contribution to the field of astronomy. He improved the telescope, which allowed him to make groundbreaking observations. One of his most notable discoveries was the four largest moons of Jupiter, now known as the Galilean moons: Io, Europa, Ganymede, and Callisto. This discovery provided strong evidence against the geocentric model of the universe, which placed Earth at the center, and supported the heliocentric model proposed by Copernicus, which placed the Sun at the center.
Galileo also observed the phases of Venus, which further supported the heliocentric model. His work laid the foundation for modern astronomy and challenged the prevailing scientific and religious beliefs of his time. Despite facing opposition and being placed under house arrest by the Roman Catholic Church, Galileo’s contributions have had a lasting impact on science and our understanding of the universe.