Galileo Galilei was an Italian astronomer, physicist, and mathematician, often hailed as the “father of modern science.” His support for the heliocentric model of the solar system challenged long-standing beliefs and made him a central figure in the Scientific Revolution. When one hears of Galileo Galilei, the telescope often comes to mind. Crucially, Galileo was among the first to turn the telescope toward the heavens, making groundbreaking astronomical discoveries that transformed science. Galileo’s first telescope, constructed in 1609, could magnify objects about three times their apparent size to the naked eye. Encouraged by this success, he quickly improved his design, creating instruments that magnified up to eight times and eventually 30 times. Although several other astronomers also began using telescopes to observe the heavens around that time, Galileo was the first to use it systematically for scientific discovery and to publish his findings.
In March 1610, Galileo released “Sidereus Nuncius” (“The Starry Messenger”), a short Latin treatise presenting his first celestial discoveries. Galileo revealed that the Moon was not a perfect, smooth sphere, as Aristotelian cosmology taught, but rather mountainous and cratered, resembling the Earth’s surface. When he turned his lens to the Sun, he discovered dark patches on its surface – what we now call sunspots – and observed that they moved, providing evidence that the Sun rotated on its axis. Among Galileo’s telescopic discoveries, his observation of the phases of Venus was particularly significant. He saw that Venus displayed a full set of phases, similar to the Moon, which could only occur if Venus orbited the Sun.
