The Copernican Revolution

This article was written by Christine (Coutts) Clement for the Thamesville Herald in honour of IYA2009.

It was published on July 15, 2009.


Jupiter's moon Europa

The picture shown here was obtained in January 1997 with NASA's [aptly named] Galileo spacecraft, from a distance of 2000 miles. It covers an area of about 6 by 10 miles across and shows an icy surface with a complex pattern of ridges and grooves.
Europa was one of the four moons that Galileo discovered when he pointed his telescope at Jupiter in 1610. But it didn't look like this when he saw it. Although Europa is almost as large as our Moon, it appears much smaller and fainter when viewed from Earth because it is more than 400 million miles away from us.
Image credit: NASA/Arizona State University

When we think of revolutions, the political events in Russia in 1917, or in France in 1789, often come to mind. But the Polish astronomer Copernicus started a scientific revolution when he published his famous book, "On the Revolutions of the Heavenly Spheres" in 1543.

In his book, Copernicus proposed that the Sun, not the Earth, was at the centre of the Universe. His conclusion was so radical at the time, that even he was afraid to publish it! The only reason the book got published was because of the encouragement he received from a young German mathematician named Rheticus.

Some thirty years earlier, Copernicus had circulated a brief outline of his ideas to a few scholars and the word had spread throughout Europe. When Rheticus heard about these opinions in 1539, he travelled to Poland to persuade Copernicus to submit his manuscript for publication. As a result of this visit, the famous book was published in Nuremberg in 1543, only a short time before Copernicus died.

In the century that followed, advances in the technology for observing stars and planets led to important discoveries that paved the way for the universal acceptance of the Copernican hypothesis.

The Danish astronomer Tycho Brahe played a crucial role. His contribution was to observe the positions of the planets and stars continuously, over a period of 20 years, with instruments that were the best in his day. His observations were the most complete and precise that had ever been made. He finished his project in 1597, before the telescope was invented.

Based on his data, Tycho proposed an Earth-centred system that included some features of the Copernican system. It was a compromise. However, after his death in 1601, a German mathematician named Kepler re-analysed the data and developed laws of planetary motion that supported the Copernican model. Kepler's laws are still used today.

In 2009, we are celebrating the 400th anniversary of the astronomical use of the telescope. When Galileo pointed his telescope at celestial objects, he began to make discoveries that illustrated that the Earth was not the centre of the Universe.

One of Galileo's first discoveries was that Jupiter had four moons revolving around it. This demonstrated that the Earth was not unique in having a moon. And when he observed the different aspects of Venus, he was able to prove that Venus moved around the Sun, not the Earth. Previously, Galileo had privately favoured the Copernican system, but after these discoveries, he acknowledged it publicly. Unfortunately this got him into trouble with the Inquisition. Even though the Jesuit astronomers confirmed his telescopic discoveries, they did not approve of his interpretation. As a result, he was sentenced to house arrest from 1633 until his death in 1642.

Later in the century, circa 1665, Isaac Newton developed his famous law of universal gravitation and it was the work of Tycho, Kepler and Galileo that inspired him. Newton showed that gravity caused the Earth and other planets to move in orbits around the Sun. His discovery marked the completion of the Copernican revolution.

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