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

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

Tycho Brahe

Tycho Brahe was next in line to help destroy the thought of the Earth as the center of the universe. In 1572, he saw a supernova in the constellation Cassiopeia. The geocentric view had held that, in addition to the Earth being the center of everything, the stars were fixed upon a celestial sphere that was unchanging.

However, Tycho did not completely disbelieve the geocentric model. He developed a system that kept the Earth at the center, but the other planets revolved around the sun in circles, which orbited Earth in a circle. This model became very popular for a while.

One of Tycho's most important beliefs was in the accuracy and number of astronomical observations. He believed that in order to truly advance astronomy, one needed precise observations of everything in order to really understand what was going on. To this end, he developed several new instruments, and periodically calibrated them in order to make sure that they were still accurate.

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 record of positions. It was through this that many orbital anomalies that had never been detected were found, and that one of his assistants was able to revolutionize astronomy with three laws.

Johannes Kepler

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. However, after many years, Kepler found that the data supported three laws that astronomers still use very often today. Kepler's three Laws of Planetary Motion are:

1. Every planet follows an elliptical orbit around the sun.
2. 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.
3. 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.