One of his achievements was discovering four new “stars” orbiting Jupiter and the phases of Venus. In 1609 he built his first telescope improving the Dutch telescope, and made other observations about the moon’s surface other stars in the Milky Way. The four new moons were called Callisto, Europa, Ganymede, and Io. When he showed his findings to the Grand Duke, Cosimo II de Medici, they were named “Galilean stars” in honoring of him.
Galileo invented the first pendulum. He started researching it while watching lamps swing as a medical student, but