If Tycho Brahe was great at raising money, and making careful observation, but not so great with theory, Johannes Kepler, who worked with Brahe in the second observatory that brahe built, near Prague, was great both at observation and at theory.
After having analyzed the orbit of Mars, following a suggestion from Tycho Brahe, Kepler realized started forming the first tow of his three rules of planetary motion in the early 1600s.
The third law of motion had to wait until the late 1610s.
Kepler was a part of the Catholic Lutheran wars of his period, and his mother was tried as a witch,
It took a while for his theories to be accepted, but today they are an important part of astronomy.
Kepler's laws are:
1. The orbit of every planet is an ellipse with the Sun at one of the two foci.
2. A line joining a planet and the Sun sweeps out equal areas during equal intervals of time.
3. The square of the orbital period of a planet is directly proportional to the cube of the semi-major axis of its orbit.