Italian scientist Galileo Galilei was not the first person to claim Earth orbited the sun. But he was the first who could prove it.
Italian scientist Galileo Galilei was not the first person to claim Earth orbited the sun. But he was the first who could prove it.
His observations made through a home-made telescope changed the course of science.
It is hard for anyone looking at the stars ‘moving’ across the heavens to accept that they are not revolving around Earth – and that our planet is itself rotating and hurtling through space.
That is why ‘geocentrism’ – the mistaken belief that the Earth is at the centre of the universe – was accepted as fact for more than 1,000 years.
The motions of the sun, moon and other planets relative to the stars had to be explained too, however – and several geocentric theories were put forward.
The most sophisticated was by Greco-Roman astronomer Ptolemy (Claudius Ptolemaeus, c.120-180 BC), in the 2nd century BC.
In the ‘Ptolemaic system’, the planets, the sun and the moon each occupied a separate rotating sphere around the Earth.
In Europe and many parts of Asia, this was assumed correct for 1,400 years.
So compelling and deepseated was the geocentric view that few people questioned it.
Universities, run by the Catholic Church, adopted Ptolemy’s system as fact.
By the late Middle Ages, anyone who dared to suggest alternative views risked being declared a heretic.
However, several astronomers, even in ancient times, had put forward ‘heliocentric’ systems – with Earth and the other planets in orbit around a central sun.
Most important was Polish astronomer Nicolaus Copernicus (1473–1543), whose influential work De Revolutionibus Orbium Coelestium (‘On the Revolution of Celestial Spheres’) was published in 1543.
His system found increasing support during the second half of the 16th century.
German astronomer Johannes Kepler (1571–1630) developed it, using geometry to show how planetary orbits around the sun must be ellipses (flattened circles).
But it was the publication of Galileo’s observations that proved crucial in its acceptance.
In 1609 Galileo (1564–1642) heard about the telescope, invented by Dutchman Hans Lippershey (1570–1619).
He had soon made his own, improved the design, and turned it to the night sky.
He observed several things that backed ‘Copernican’ theory – in particular, moons in orbit around Jupiter.
Clearly, he thought, not everything revolves around the Earth.
He also saw that Venus has phases like those of the moon – that could only happen if it was moving around the sun.
In 1610 he published a small book called Sidereus Nuncius (The Starry Messenger) in which he explained his observations.
Galileo quickly became a champion of the heliocentric view. He also uncovered evidence against the prevailing view that the heavens were perfect: craters on the moon and spots on the sun.
At first, Galileo found favour with high-ranking Church officials. But in later publications he ridiculed the Church’s teachings.
He was commanded not to support the heliocentric view.
In 1633 he was called to Rome, where he faced the Inquisition. His books were banned and he spent the rest of his days under house arrest.
In the 1680s, English scientist Isaac Newton showed how gravitational forces could explain the planets’ orbits around the sun.
His Law of Gravitation gave mathematical support to the heliocentric view.
At last, astronomers could use equations to predict the motions of the planets – in their orbits around the sun - with unprecedented accuracy.
