It was Johannes Kepler in 1618.
Ellipse.
kepler
Kepler discovered that the orbit of each planet is an ellipse rather than a perfect circle. The planet with an orbit that is closest to a circle is Venus.
Ellipse..
Kepler
The sun is located at one of the focii of the ellipse that describes the orbit of a planet. The focus of an ellipse is not in the geometric center but on the major axis of the ellipse.
This particular innovation was made by Johannes Kepler, which resulted in the observations of the planets finally falling precisely into the calculations that were made with the heliocentric theory.
The path is called an "orbit", and it has the shape of an ellipse, the Sun being at one focus of the ellipse.
This orbit is called an ellipse. An oval shape.
He discovered that avery planet has a ellipcial orbit, which means oval.
Planets remain almost perfectly spherical as they move around the sun. The paths they follow are ellipses, with the sun at one focus of each ellipse.
That's the definition of an ellipse.