Kepler

Johannes Kepler
Astronomia Nova
De Stella Nova

The astronomer Johannes Kepler (1571-1630) defended the Copernican heliocentric views and is well-known for his laws of motion. He was very concerned with finding harmonies in nature. He also created astrological calendars and the Rudolphine Tables, which included data of use in determining planetary positions.

Kepler is particularly important for discovering that the orbits of the planets are elliptical.  This represented an important advance.  The ancient astronomers believed that the circle was the most perfect shape and the heavenly bodies must therefore have perfectly circular orbits.  This understanding of the planets moving in perfectly concentric circles was a key component of the Ptolemaic understanding of the universe.  Careful attention to observational data about planetary motion let Kepler understand that the true orbits are ellipses.

In his book The Eye of Heaven: Ptolemy, Copernicus, Kepler, the historian of astronomy Owen Gingerich writes the following:

"When Kepler arrived in Prague, he bet... that he could solve the theory of Mars within a week. He lost the bet, of course -- it actually took five years, but, as he apologized in the Astronomia nova, he took one year out for optics. His resultant work, the Astronomiae pars optica, lays the foundation for modern geometrical optics. In it he explains, for the first time, how an inverted image is formed on the retina of the eye, and he clearly defines the light ray."

Gingerich notes that it has been argued that Durer's work on perspective may have influenced Kepler's exploration of image formation.