how did kepler know that orbits of planets are elliptic?

Question

i searched everywhere but they only say that kepler stated that

Answer 1

Kepler had access to astronomical data taken by Tycho Brahe on planetary motion the latter took during his work as some prince's astrologer (yes, astrologer). Kepler believed on ideological grounds that planetary motion should be described by simple mathematical formulas. Prior efforts to do this involved use of epicycles (compound uniform circular motion, or "wheels within wheels"). Tycho's data exceeded in precision everything before it (without use of a telescope, btw), and it became clear that too many epicycles would be needed to fulfill Kepler's desire for simplicity. So he tried an ellipse, which is only slightly more complex than a circle. The data fit, and the rest is history. Kepler did not believe it was possible to provide any deeper explanation for his laws of planetary motion. That had to wait for Newton.

The Internet has its purpose, but if you're interested in learning more about Kepler and other astronomers of this time, I recommend the referenced book. You remember, portable cellulose format.

Answer 2

i am going to't imagine of a few thing except that the planets and really some asteroids are interior an same orbital plane. you won't be able to say that about comets and many don't actually have elliptical orbits.

Answer 3

Are you looking for a mathematical proof?

There is a proof in my reference using basic calculus notions if that is what you are looking for.