Kepler’s First Law of Planetary Motion
Kepler’s laws of planetary motion, in astronomy and classical physics, laws describing the motions of the planets in the solar system. They were derived by the German astronomer Johannes Kepler, whose analysis of the observation of the 16th century Danish astronomer Tycho Brahe enabled him to announce his first two laws in the year 1609 and a third las nearly a decade later, ion 1618. Kepler himself never numbered these laws or specially distinguished them from his other discoveries.
What is Kepler’s first law?
Kepler’s First Law: The planets move around the Sun in an elliptical orbit with the Sun at one focus of the ellipse.
The orbit of a planet about its star (the sun for our solar system), follows an elliptical path with the star occupying the position of one of the foci of the ellipse formed.
As mentioned in the short biography of Kepler, his first law was a result of a great insight that planets did not necessarily move in perfect circular orbits, which had been long assumed. Using Tycho’s measurements of the motion of Mars across the sky, Kepler discovered planets move in elliptical orbits with the sun not at the centre of the ellipse, but at one focus (the other focus is empty). It’s a deceptively simple law that took astonishing insight and five years of hard work.