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Essays for amateurs and professionals interested in  Science


    the foundation for community access to science Henry Mulder
[1939-2009]
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Tycho Brahe and Johannes Kepler
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Image courtesy of NASA


Image courtesy of NASA


Image courtesy of NASA


Image courtesy of NASA


Feature Article
Tycho Brahe and Johannes Kepler (ESS21)

Their Contribution to the understanding of the Universe


Written by...

"The Universe is infinite and infinitely mysterious and like Newton we can only amuse ourselves with smoother pebbles and prettier shells."*

In 16th Century Europe, science stood at the cross-roads. Much of the scientific investigation of the day had to do with astronomy, the study of the heavens. And there was the problem. As we have said elsewhere, the prevailing ideas about the planets, stars, etc. were strongly influenced by Aristotle's view of the heavens. In this view, there was a distinct separation between the heavens and the earth, or more specifically, the heavenly sphere and the earthly one.


Photo credit NASA
Tycho Brahe
The heavenly sphere which consisted of the fixed stars and the planets was thought to be perfect and unchanging as God had intended and everything inside the orbit of the moon was thought to be of the earthly sphere with all its messy bits. One person to change all that was a hot-headed, hard-drinking, disagreeable, tyranical Dane with a passion for accuracy and an all-consuming interest in the heavens. His name was Tycho (pronounced 'Teeko') Brahe (1546-1601). Not to put too fine a point on it, he was a real party animal with a penchant for brawling.

By 1543 Nicolaus Copernicus' work on the helio-centric (sun-centered) nature of the Universe had already been published but Galileo had not yet discovered the moons of Jupiter or the phases of Venus. Copernicus' ideas were not universally accepted and were mostly suppressed. So when on November 11, 1572 Brahe noticed what appeared to be a new star in the heavens, it made an enormous impact. The new star was so bright that it could be seen in broad daylight. It was what we now call a nova, which even today is a pretty rare event.

The Beginning of Doubt
So Brahe spots a nova, so what? Remember, in 16th century Europe, the belief in Aristotle's eternal unchanging firmament was held to be the absolute truth. Therefore this new phenomenon which spelled out change in a big way, had to be located in the imperfect earthly sphere. What if it wasn't and how could you tell?

It was held that the stars were fixed in place in the heavens, placed there by the Almighty himself, while other bodies in the sky had a tendency to move about. If it could be shown that this new "star" also moved around in the heavens that would place it squarely below the realm of the unchanging stars and all would be well.

It was assumed that this could be easily shown so when a few astronomers of the day made a crude attempt to detect movement in this new "star" and found none, the stardust really hit the fan. But wait. Because their methods were not overly accurate, it could still be argued that there might be movement, just not enough to detect.

This is where Tycho Brahe's penchant for accuracy became the key issue. He had just finished building a new sextant, with arms five and a half feet long, a massive bronze hinge, a metallic scale calibrated in minutes (sixtieths of a degree) and a table of corrections for the remaining tiny errors in the instrument he had detected.

With this marvelous instrument and his insistence on absolute accuracy, he was able to settle the argument. The new star did not move at all relative to the fixed stars. This proved without a doubt that the new star was indeed in the heavenly realm. At a stroke, Brahe proved that Aristotle, and all the schoolmen who accepted his vision, were wrong. The heavens were not the never changing realm that all the Christian scholars said it was.

Not everyone was convinced though, especially not the official church. Even with this elegant proof, Galileo, for example, still ended up in trouble partly because of his suggestion that things in the heavenly realm were not divinely "perfect" and unchanging. Officially of course, Galileo's major "sin" was his acceptance and promotion of the Copernican suggestion that the earth was not the stationary center of the universe.

Even Brahe himself had a problem with that one and he was never able to completely embrace the idea that the earth was not the center of the universe but moved around the sun. In any event, demonstrating that a key element in Aristotle's astronomy was wrong as shown by the new star in the heavens, did raise some serious questions about the rest of the bible-sanctioned cosmology of the church. In time, that would lead to the kind of conflict between religion and science that we still see today.

Tycho Brahe's Legacy
For a detailed look at Tycho Brahe's life and times you can go to this entertaining and informative website. Here you can read about his tempestuous associations with his family, his associates and the various members of royalty with which he was involved. You can read about his affluent lifestyle which his noble birth and royal favors afforded him. Here too, you can read about his artificial nose made of a gold and silver alloy, and how he came to lose his real one in the first place.

What is of interest to us here are those wonderfully detailed star charts he produced during a lifetime of dedicated stargazing. All the more amazing because it was all done with only the naked eye, since the telescope had not yet been perfected. In order to accomplish this staggering feat, Brahe constructed various instruments, which in spite of their large proportions were nevertheless extremely accurate.

This accuracy was key because an early interest in the stars had shown him that all the charts available up till that time contained many errors caused by sloppy observation. He concluded quite correctly that these errors made it impossible to gain an accurate understanding of how the universe actually worked. Ironically, although his careful measurements led him to a very accurate picture of heavenly motion, he could not bring himself to fully embrace Copernicus' idea that the earth was not the center of the universe.

He quite correctly placed all the heavenly bodies in their proper place revolving around the sun. Nevertheless he kept the earth as the center of the whole system for two reasons. For one thing, having the earth too, revolve around the sun would contradict the Bible. In addition, as he reasoned quite correctly, since he could not detect any evidence of stellar parallax even with his highly accurate measurements, the earth couldn't possibly be revolving around the sun. What the heck was this "stellar parallax"?

Where's the Parallax?
A very good question. Imagine for a moment, that you are looking at a particular star and are able to measure the exact angle at which it is situated in the heavens in relation to neighbouring stars. Now imagine you are looking at this same star six months later. If you accept the fact that you are revolving around the sun, you should now be at the opposite end of the earth's orbit. That being the case, the apparent angle should have changed if only a little. Although the angles did in fact change, even with his vastly superior methods, he just couldn't measure that change. In his mind that proved the earth stood still in the heavens.

Never mind this little detail. Parallax was eventually confirmed, but that's another story. A lot of Brahe's work was carried out in his fanciful Uraniborg castle on the Danish island of Hveen begun in 1576. This idyll lasted until 1597 when for a number of reasons he decided to relocate. He gathered up his family and all his belongings and eventually ended up in Prague, in present-day Hungary in 1599. It was there in 1600, that he and Johannes Kepler got together to continue the work.

Johannes Kepler
Johannes Kepler was born on December 27, 1571 in Weil,

Photo credit C. H. Beck, 1937 (NASA)
Johannes Kepler
Germany close to the French border. Unlike the robust Brahe, Kepler was sickly from birth. His vision was severely defective, and he suffered various other illnesses on a regular basis. School for him was difficult, especially at the elementary level. He did a little better when he got to the higher school at Maulbronn. By the time he got to the (Lutheran) University of Tuebingen he began to blossom and here his exceptional intellectual abilities began to show.

One of the reasons was no doubt his admiration for his math instructor Professor Michael Maestlin. Maestlin was the astronomy professor at Tuebingen. He publicly taught the Ptolemaic scheme of the heavens, but privately, he believed Copernicus. It seems the Lutherans were no more sympathethic to the views of Copernicus than the church of Rome. In fact, Martin Luther is famously quoted (referring to Copernicus) as saying: "This fool wishes to reverse the entire science of astronomy; but sacred scripture tells us that Joshua commanded the sun to stand still, and not the earth."

At Tuebingen, Kepler studied mainly theology and philosophy, but also mathematics and astronomy which ultimately became his primary interest. With the impetuousness of youth, young Kepler was quite public in his support for the Copernican system. Needless to say, this pretty much reduced his chances for a posting at Teubingen to zero. Instead he ended up accepting an astronomy professorship in Graz, in present-day Austria.

At the time, there was still considerable overlap between astronomy and astrology, which created some interesting dilemmas for the young scholar. You can read about this and many other interesting facets of Kepler's life at this website. Our main interest here is his developing interest in the orbits of the planets and how this eventually got him together with Tycho Brahe.

Even with the sun taking the place of the earth at the center of the universe, Kepler, just like Copernicus himself, was still very much inclined to see the universe in terms of a divinely assembled mechanism. He accepted the spherical orbits of Aristotle as well as seeing the whole as a clever mathematical celebration of God's glory. Kepler became more and more intrigued by the mathematical relationships of the various orbits. To confirm his ideas he needed accurate star tables and charts and we know who had those don't we. Good old Tycho Brahe.

A religious conflict in Graz led, in 1598, to his becoming unemployed as astronomy professor. The archduke, running the place, happened to prefer catholicism so the protestant university was shut down. Kepler's interest in Tycho Brahe's star tables had brought him in touch with the irascible Dane. Since he was looking for work, Tycho offered him a job in 1600. His joy at this little bonus was a bit short-lived because he soon found that getting hold of the tables wasn't going to be easy. Brahe had his own pet theories to prove so he was not all that anxious to help Kepler with his.

Nevertheless, things sort of worked out. This was in part because the great man's rambunctious life-style caught up with him and he died only a year later in 1601 which gave Kepler an opportunity to "acquire" those valuable charts. Some say he stole them. Be that as it may, Kepler now had a chance to test out his theories using the most accurate measurements ever assembled. Using these he discovered that all the theories proposed thus far, including his own, were wrong.

The Magical Ellipses
Exactly what the problems were gets a bit complicated but can be seen in greater detail in this website. After many false starts and operating in a complete unknown, hampered by the actively hostile society of his day, Johannes Kepler eventually came up with the right answer. The orbits were not round or even oval. They were ellipses. Not only that, but the velocity of those orbits was constantly changing in an elegant rhythm of faster and slower.

As clever as these insights were, Kepler like so many others who contributed to our present knowledge of our world, was also wrong about some things. For example he surmised that the planets needed and received a constant push, much like the Aristotelian model, but that this emanated from the sun. On the other hand he did conclude that tides were somehow caused by the action of the moon. This notion was flatly rejected by Galileo who had come up with his own curious cause for the tides. Mind you Galileo was also never able to give up the idea of divinely perfect circular orbits either.

When Isaac Newton in the latter part of the 17th century came up with his idea of inertia and universal gravitation to explain what made the planets move the way they did, it was the meticulous work of first Tycho Brahe and subsequently Johannes Kepler that allowed him to sort it all out. This is an often repeated story. Nobody ever comes up with the whole answer by themselves. But every so often, there are individuals who, without necessarily meaning to, turn accepted scientific beliefs on their head.

Tycho Brahe was certainly one of those. Kepler was another. In looking at their accomplishments, I'm always reminded of that well-known line from a John Lennon song: "Life is what happens when you're planning something else." We have to admire those who like Kepler, were honest enough to discard dearly-held ideas when the evidence pointed in a different direction. This is doubly true if you also consider the often hostile attitude of those around them who wished to at-all-cost defend the status-quo.

Finally, the pursuit of knowledge is rarely straight-forward and is often messy. Isaac Newton for example, was heavily into Alchemy and the occult. It is sometimes thought, that his belief in the supernatural made it easier for him to accept an almost magical force—gravity—that was able to act through a void over great distances. Who's to say?


*Isaac Newton is famously quoted: "I do not know what I may appear to the world, but to myself I seem to have been only like a boy, playing on the seashore, and diverting myself in now and then finding a smoother pebble or a prettier shell than ordinary, while the great ocean of truth lay all undiscovered before me."

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