February 19, 2010

Happy Birthday, Nicolaus Copernicus




This German/Polish polymath (a person who is learned in many different fields) was born on this day in 1473. He was a mathematician, astronomer, doctor, translator, artist, Catholic clergy, jurist (one who studies, develops or applies the law), governor, military leader, diplomat and economist. He was a polyglot as well, speaking German, Latin, and Polish with equal fluency and also Greek and Italian.

During his lifetime, Copernicus might have been known to many as his powerful uncle's personal secretary, perhaps, or as the published translator of some poems written in Greek. However, we know him today from his contributions to astronomy and, more generally, to science.

Even though astronomy was just a sideline for Copernicus, he was able to work out the heliocentric, or sun-centered, model of the solar system.

For thousands of years it was thought that the Earth sat still at the center of the universe, and everything people could see in the sky, from the Moon and Sun to the planets and stars, circled around it. People thought this was true because we experience the world this way—as we stand on the Earth, we do not feel as if it is in motion, and we clearly see the Moon, stars, and Sun moving in our skies.

However, in order for our observations of the observed movements of the planets to make sense, we cannot suppose their paths around the Earth to be simple circles. Instead, thinkers like Ptolemy invented little circles cycling around larger circles—epicycles, deferents, and equants—in a very complicated system.

Copernicus demonstrated that, by simply moving Earth out of the central spot and supposing that it was in motion, too, most of those complications fell away.

Copernicus's system started with the idea that the Sun is the unmoving center of the universe. Mercury and Venus circle the Sun in closer orbits than the Earth's, and Mars, Jupiter and Saturn circle the Sun in farther orbits. According to Copernicus's model, the firmament doesn't move; this outermost celestial sphere was pictured as a sort of rigid shell onto which the unchanging stars were attached.

The fact that the unmoving sun and firmament (the stars) seem to move around the Earth once per day was explained, in the new Copernican system, by the idea that the Earth itself is spinning around like a top, rotating on its axis once a day. So the Earth has two motions—spinning on its axis and revolving around the sun.

You probably noticed...
...Hopefully you noticed that Copernicus wasn't entirely correct in every aspect of his heliocentric model of the universe.* However, he was correct that the sun was the center of the solar system, and this Big Idea was so important to astronomy, science and philosophy, that scientists have credited him with starting a scientific revolution!

*The sun is not actually the center of the universe. It's pretty far out from the center of the Milky Way galaxy, even, hanging out in an obscure corner of one of the spiral arms. Nor is the Milky Way galaxy the center of the universe. As a matter of fact, the phrase “the center of the universe” might not even make sense.

Also, there is no firmament. There is no solid shell or sphere onto which stars are glued. Instead, the stars are much larger and much farther away than they seem, great balls of burning gas similar to our sun, and they are at all different distances away from us. Stars—even our sun—are in motion, too, revolving around the center of their galaxies even as the galaxies rush away from each other. Also, the stars certainly aren't unchanging—new ones are born, older ones die.

Finally, of course, there are many bodies in the solar system that Copernicus didn't know about, most noticeably two more planets, Uranus and Neptune.

Ahead of His Time
Copernicus's Big Idea was a bit too radical for most people of his time, and for more than a century, most people didn't accept it. Remember, some of Galileo's findings confirmed the Copernican system, but he was put on trial and then under house arrest because of it—and that was 100 years later!

Watch a short video about Copernicus.
With the animated sequences about orbits, this one makes Copernicus's Big Idea easy to understand.

Read more about Copernicus's Big Idea.
This website explains the Sun-centered system with words and diagrams.

Copernicus has been honored with many memorials, with his face on Polish money, with a crater on the moon named for him, and most recently with a new element (atomic number 112) named copernicium.