Here's why:

* Kepler's Laws of Planetary Motion: Johannes Kepler, through careful observation, determined that planets orbit the sun in elliptical paths, not perfect circles.

* Focus Points: An ellipse has two focus points. The Sun is located at one of these focus points, not the center of the ellipse.

* Orbital Speed: A planet's speed varies as it orbits the sun. It moves faster when closer to the sun and slower when farther away. This variation in speed is a characteristic of elliptical orbits.

Let me know if you'd like to delve deeper into the details of elliptical orbits or Kepler's Laws!