Johannes Kepler and Tycho Brahe

Tycho Brahe (1546-1601) and Johannes Kepler (1561-1630)

The Church and Copernicus | Galileo Galilei | Tycho Brahe and Johannes Kepler | Isaac Newton

Before the invention of the telescope, Tycho Brahe observed the positions of the planets, Sun, and nearly 800 stars to an unprecedented accuracy. He was born in the Danish province of Skaane into a powerful noble family. It was assumed that Brahe would eventually become a soldier or an administrator for the king. He enrolled as a law student at the University of Copenhägen, but several celestial events that he witnessed changed his career path forever.

The first event was the solar eclipse of 1560. Tycho was amazed that astronomers were able to predict such events in advance. The second was a conjunction of Jupiter and Saturn. It was the latter event that convinced Tycho that he should devote his life to studying the sky, for the published tables that predicted the event were grossly inaccurate, missing the actual conjunction by several days.

Tycho Brahe Finally, he saw the supernova in the constellation Cassiopeia of 1572. He later wrote in his book De Stella Nova ("On the New Star"), "I noticed that a new and unusual star, surpassing all the other stars in brilliancy, was shining almost directly above my head. And since I had almost from boyhood known all the stars of the heavens perfectly ... it was quite evident to me that there had never before been any star at that place in the sky, even the smallest, to say nothing of a star so conspicuously bright as this."

Church dogma of the times forbade any changes to the perfect celestial sphere, so anything that was new must be atmospheric phenomena. However, Tycho reasoned that if it were atmospheric, then it would display a parallax, which it did not. He firmly stated, "I conclude that this star is not some kind of comet or fiery meteor ... but that it is a star shining in the firmament itself -- one that has never previously been seen before our time, in any age since the beginning of the world."

Tycho's heresy moved him to the position of the leading astronomer of the times. The Danish King, Frederick II, also took notice of Tycho's fame, and wished to keep him close to home to glorify the country. In 1576, Frederick II offered Tycho his own island and funding in the channel between present-day Denmark and Sweden, where Tycho could pursue his mapping goals.

Tycho and his assistants transformed the 5 km (3 mile) long island, Ven (old Danish is Hven), into Europe's center of astronomy. His laboratory was known as Uraniborg ("Heavenly Castle"). But, this was too unsteady for Tycho's needs, so he built a second observatory across the road from it, named Stjerneborg ("Castle of the Stars"), with a foundation deep into the ground to steady the building. Historians estimate that Uraniborg received 1-1.5% of the Danish national budget.

The most well-known of Tycho's instruments was a mural quadrant. Its radius was more than 1.8 m (6 ft), and occupied an entire wall that was oriented precisely North-South. The altitude of objects that passed into view on the wall's plane could be measured to an precision of about 10 arcmin.

His observations were the best anyone had ever been able to make before. He increased the accuracy of position measurements to over seven times more precise than they had been, and some of his most accurate observations were 30 times more accurate than those of previous astronomers. Besides accuracy, though, Tycho was interested in the shear number of observations. While previous astronomers were content with observations a few times in a planet's orbit, Tycho kept almost continuous records of positions. It was through this that many orbital anomalies that had never been detected were found.

However, with the death of Frederick II and the rise of Christian IV, Tycho lost his good standing in Denmark. Other nobles were jealous of Tycho's good standing, and the new king wished to concentrate power in Copenhägen, questioning the huge expenditures to Ven. Also, Tycho neglected his responsibilities as a nobleman, which - among other things - included the maintenance of the cathedral in Roskilde. Its leaky roof threatened to mar the tombs of the king's father and grandfather.

In 1599, Tycho left Denmark and came under the grateful wing of Emperor Rudolf II of Prague. "Tycho came to Prague as a leading person in his field. His position in the court and his salary confirm that he was highly appreciated by the emperor," says Pedr Hadrava, an astrophysicist with the Czech Academy of Sciences.

It was in Prague that Tycho developed a new model for the solar system. He did not completely believe the geocentric model, but he didn't completely disbelieve it, either. He proposed a system that kept the Earth at the center, but the other planets revolved around the sun in circles, which in turn orbited Earth in a circle. It was the "common sense" stability he felt in Earth and the absence of observable stellar parallax that prevented him from making the leap to a completely heliocentric vista.

It was in Prague that he became the mentor of Johannes Kepler, who came to inherit Tycho's volumes of data.

One of Tycho's assistants, Johannes Kepler, was given records of the planetary positions. Hundreds of pages of data took a very long time for Kepler to sort through. Yet Kepler's knack for mathematics - something his mentor did not posses - allowed Kepler to develop his three laws of planetary motion - laws that are still in wide use today. Kepler's three Laws of Planetary Motion are:

Every planet follows an elliptical orbit around the sun.
An imaginary line from the center of the sun to the center of a planet sweeps out the same area in the same given time. One way of understanding this is by picturing it as planets move faster when they are closer to the sun, so even though they are closer so the area they sweep out would seem less, it is the same because in the same time frame the planet covers more distance.
The square of a planet's period (year) is proportional to the cube of its distance from the sun:

Besides their usefulness in astronomy in the past and today, Kepler's Laws added more of a mathematical framework to the heliocentric model of the universe, and so added even more fuel to the Copernican Revolution. After all, the Scientific Revolution wanted everything to be based in observation and testable and provable hypotheses.