Galileo Galilei, born 15 Feb 1564, has been described as the “Father of Modern Science”. His observations helped provide important evidence for the heliocentric theory and to destroy the Aristotelian notion of the “unchanging perfection of the heavens”. He also promoted the idea that the laws of nature are mathematical in nature. His rejection of philosophical and religious authority in favour of experimental results helped to separate science from philosophy and theology.
In January 1610 he observed three “stars” near Jupiter. Over the next few nights, he observed that they were not fixed but were actually moving around Jupiter. He realised that they were satellites of Jupiter, and also observed a fourth – thus discovering Io, Europa, Ganymede and Callisto. Over the next months he continued to observe these moons, accurately estimating the periods of their orbits.
He was the first to observe craters and mountains on the moon, and estimated their heights. He also observed sunspots, which had been previously observed but mistaken for the transit of Mercury.
With his telescope, which he gradually improved to offer 30x magnification, he observed many new stars invisible to the naked eye, and also saw Neptune (but mistook it for another star). Not only did he work on developing the telescope, he also improved the design of the compass and the microscope.
Galileo was not without his flaws. For example, in his desperation for evidence that the Earth rotated the sun, he uncritically accepted arguments that the Earth’s movement caused tides, rejecting Kepler’s theory that tides were caused by the moon. He also rejected the elliptical motion of the planets, preferring circular motion.
Nonetheless, Galileo was without doubt one of the great founders of modern science, and today we celebrate his 445th birthday.
This year is also the 400th anniversary of Galileo demonstrating his telescope, and is being celebrated in the International Year of Astronomy. One of the projects of the IYA is the 365 Days of Astronomy podcast – if you’re not listening to it already, you really should be.