I'm pretty sure you're thinking of Johannes Kepler.
Johannes Kepler
Kepler defined the basic laws of orbital motion, and these naturally had to be calculated.
That is one of Kepler's Laws, stated by Johannes Kepler.
Kepler discovered that the planets move in elliptical orbits and he published three laws of planetary motion that explained the details of the ellipses. Kepler's work used observations done by Tycho Brahe, and subsequent observations confirmed that Kepler's laws were correct (they still are). No-one knew why until the later discoveries of the laws of motion and the laws of gravity about 70 years later.
No. Kepler discovered the laws using Tycho Brahe's data.
Johannes Kepler is credited with forming the mathematics of elliptical orbits.
All 3 of them (Kepler's laws of planetary motion).
The general laws about the planets' orbits were known before Newton - mainly, through the three Laws of Planetary Motion, by Kepler. Newton showed that the movement - as explained in Kepler's Laws - was a result of the laws of motion (especially Newton's Second Law), and of the force of gravitation.
"Eponymous" means "Same name". The laws of planetary motion were devised by Johannes Kepler, and are generally called "Kepler's Laws".
Kepler's Laws describe what happens. Newton's Laws describes what happens and why. The why is the theoretical explanation due to Gravity.
I'm pretty sure you're thinking of Johannes Kepler.
Johannes Kepler
The laws are known as Kepler's Laws after German mathematician and astronomer Johannas Kepler (1571-1630).
No, Johannes Kepler is best known for describing the laws that dictate how orbits work. The Kepler planets were discovered by the Kepler telescope, a spacecraft named in his honor.
No. Kepler died before Newton was born.
His laws of planetary motion.