There have always been dangerous topics – ideas and
points-of-view that can get you in trouble with the authorities or with other
people. In every society it’s important to know the rules about what you can
say to who. But it’s hard to believe that those topics used to include the sun,
planets and stars.
How could it be dangerous to talk about the sky? Nicholaus
Copernicus could have answered that. He was a Polish cleric, mathematician and
astronomer who was born on this day, 19 February, in 1473. And he supported a
dangerous idea: heliocentrism. That’s the fancy word for the theory that the
earth goes around the sun, rather than the other way around.
Heliocentrism was a dangerous idea because the churches
opposed it. Everyday experience tells us that the earth stands still and that
the sun moves around it, rising in the east, setting in the west. Science now
teaches us otherwise, but for a long time astronomers agreed with everyday
experience: the earth is still, the sun moves. Copernicus was born into a
geocentric universe, or one that had the earth at its centre. This is certainly
what the Bible seems to teach: the Old Testament talks about a miracle in which
“the sun stood still” for “a whole day”. How could that be a miracle unless the
sun is usually moving?
That was how educated people reasoned hundreds of years ago,
so Copernicus was cautious about promoting his heliocentric, or sun-centred,
theory. His book discussing the theory, On the Revolution of the Celestial
Spheres, wasn’t published until the year of his death in 1543. He wanted to
be safely underground if his ideas caused trouble. But his theory had been
publicized and discussed a long time before that. And it did get someone else
in trouble: the great Italian scientist Galileo would later be put on trial and
placed under house arrest for supporting a stationary sun and moving earth. He
was a more fiery and abrasive character than Copernicus, and he didn’t have an
official position in the church.
Copernicus wasn’t the first astronomer to suggest that the
earth went around the sun, because the Greek astronomer Aristarchus of Samos
had done that more than 2000 years ago. But most astronomers had always
supported common sense: the earth is still, the sun is moving. The problem is
that geocentrism makes calculating the movement of the planets difficult. If
they move in perfect circles, which all astronomers then believed, why do they
sometimes seem to move backwards against the stars?
To make the geocentric theory fit what actually happened in
the sky, astronomers had to make their models more and more complicated, adding
circles onto circles. Copernicus too believed that the planets moved in perfect
circles, so his theory too had its complications, but it was still a great
advance on the old system.
It was also a very important step in the creation of modern
science and of the modern world. Before Copernicus, the earth seemed the most
important place in the universe. After all, it was at the centre. It was the point
around which everything else revolved. After Copernicus, when his ideas had
become widely accepted, all that changed. The earth was not at the heart of the
universe any more. It had lost its literally central place in the scheme of
things. The Copernican revolution, as it is now widely called, didn’t only
transform science: it also transformed culture and psychology. Heliocentrism
truly was a dangerous idea.