Galileo Galilei

There was a time when priests decreed the laws of science. That was what was happening in Italy and much of the rest of the WAlthough the Renaissance was at its height, it had not led to a liberation in scientific thought. In fact, the Catholic Church – in its Counter-Reformation against the rise of Protestantism – was doing everything it could to keep a grip on its power. The Inquisition, the threat of excommunication and the very real risk of execution – the Church would burn the philosopher Giordano Bruno in Rome in 1600 – they all helped keep potential heretics in their place.
No matter how good your ideas, it was simply not possible to disagree with the Church's view of nature, which was based on the theories of Aristotle (384–322 BC) and Ptolemy (2nd century AD). In the astronomy of the latter, the Earth sat at the centre of a perfect universe, with the heavenly bodies, including the Sun, circling round it, perfect spheres in the celestial dome. And Aristotle's physical laws were also holy writ.
So, when a young, outspoken Italian named Galileo Galilei began contradicting the Church's teachings via his experiments and observations, it was sure to cause a stir.
Chandeliers and pendulums
Galileo did not have an easy start in life. His father Vincenzio Galilei claimed to be of noble birth, but he was simply a musician, one who constantly argued with his patrons about the mathematics behind musical harmony and the rhythms of nature. Such arguments, while perhaps stimulating the young Galileo's mind, tended to reduce patronage, and the family was always short of money.
Galileo was first educated by monks. Then, Vincenzio, hoping that his son might make a better life for himself, decided that Galileo should study medicine. In 1581, at the age of 17, he entered Pisa University, his family having previously moved to Florence.
Legend has it that, during his first year at the university, Galileo noticed a chandelier, suspended from the ceiling in the cathedral, swinging in the wind. By counting the timing of each swing using the beats of his pulse, he observed something that no one had realised before: the time it takes for a pendulum to swing to and fro is the same regardless of the length, or amplitude, of the swing – a property we now call 'isochronism'. This discovery, although probably apocryphal in the detail, would lead to the development of accurate timekeeping regulated with a pendulum.
Birth of the 'wrangler'
Galileo quickly grew bored with the quackery that was 16th-century medicine. The more he observed the world and listened to what he was being taught, the more he realised that something was sorely amiss with 'science'. Just as his father saw that rigid theory was muffling new musical forms, so his eldest son came to see the Aristotelian view as restraining scientific inquiry. But tact was not Galileo's forte. His fiery arguments, quick-witted retorts and quarrels with colleagues and professors led them to nickname him the 'wrangler'.
When Galileo ran out of money in 1585, he dropped out of university to follow his interest in mathematics and science. He returned to Florence, got a position as a lecturer at the Florentine Academy and began inventing in his spare time. His hydrostatic balance brought him early fame, while his 1589 theory of the centres of gravity won him the honourable, albeit poorly paid, post of mathematics lecturer at Pisa University. He remained there for three years and then, in 1592, moved on to a mathematics professorship at the University of Padua, where he flourished for 17 years.
It was during this period that he made a concerted attack on Aristotle's theories on motion that then prevailed in physics. This resulted in his .
From the Earth to the stars
Galileo began to regard Aristotelian philosophy and Ptolemaic astronomy with increasing unease. In 1609, when he heard about a new device that could make distant objects appear closer, he reasoned it might help him study the heavens and so settle his mind. He improved on the original Dutch design of the telescope and began looking skywards.
He saw that the surface of the Moon was not smooth and perfect but full of craters, and realised that the Milky Way was made up of countless stars, none of which was orbiting the Earth. He saw spots marring the surface of the Sun, and crucially observed moons orbiting Jupiter. This last discovery had a profound effect on him. If the Earth truly was at the centre of the universe with all the heavenly bodies circling it, as Ptolemy claimed, how could some of them be spinning around Jupiter?
Galileo rushed into print in 1610 with his book The Starry Messenger. The papal court was at first impressed, despite the fact that Galileo had contradicted Ptolemy and implied that the theory of the Earth orbiting the Sun – propounded by the Polish astronomer Copernicus in 1513 – was true. estern world when Galileo Galilei was born in Pisa in 1564