How did Tycho Brahe’s observations help Johannes Kepler?

Tycho Brahe’s extensive and highly accurate observational data were essential to Johannes Kepler’s development of his laws of planetary motion.1

After Tycho’s death in 1601, Kepler gained access to his records, which included over 20 years of precise measurements of planetary positions, accurate to approximately 2 arc minutes. Kepler initially sought these values to refine his own cosmological theories, but he found that he could not reconcile the data with traditional circular orbits or Ptolemaic models.12

Specifically, while studying the orbit of Mars—which possesses a large enough eccentricity to make deviations from a circle detectable—Kepler discovered that his models failed to match Tycho’s observations by about 8 minutes of arc. Trusting the superior accuracy of Tycho’s data, Kepler was forced to abandon the assumption of uniform circular motion. This led him to conclude that planetary paths are ellipses with the Sun at one focus, forming the foundation of his revolutionary work, Astronomia Nova.1