How did Johannes Kepler do his calculations of orbital motion without the use the instruments we have available today?
Kepler was a student of Tycho Brahe who used new (at the time) instruments to measure angles and positions of objects in space. There were no telescopes at the time so all of this was done by eye. Tycho gathered a vast amount of data for the time. Kepler used Tycho’s data, mathematics and the concept of force to figure out that planets have elliptical orbits.
