Kepler's First Law states that the orbit of a planet around the Sun is an ellipse with the Sun at one of the two foci. This law is also known as the Law of Ellipses and describes the shape of planetary orbits.
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Kepler's First Law was formulated by Johannes Kepler in the early 17th century.
The elliptical shape means that planets are sometimes closer to and sometimes farther from the Sun during their orbit.
The point where a planet is closest to the Sun is called perihelion, and the point where it is farthest is called aphelion.
The eccentricity of an orbit determines how elongated it is; an eccentricity of 0 corresponds to a perfect circle.
Kepler's laws were based on precise observational data collected by Tycho Brahe.