Here's why:

* Not perfectly circular: While often depicted as perfect circles, planetary orbits are actually slightly oval-shaped.

* Focus points: An ellipse has two focus points. The Sun is located at one of these focus points.

* Varying speed: As a planet orbits, it moves faster when it's closer to the Sun and slower when it's farther away. This is due to the gravitational pull being stronger closer to the Sun.

It's important to note that while the planets have elliptical orbits, they are very close to circular. This means they are only slightly elongated.