The orbit of the Earth around the sun is almost circular, but not perfectly so. It's slightly elliptical.

Here's why:

* Eccentricity: The shape of an orbit is described by its eccentricity. A perfect circle has an eccentricity of 0, while a highly elliptical orbit has an eccentricity close to 1. Earth's eccentricity is very low, about 0.0167.

* Perihelion and Aphelion: Earth's orbit means that it's not always the same distance from the sun. The point where Earth is closest to the sun is called perihelion, and the point furthest away is called aphelion. This difference in distance isn't huge, but it does mean the orbit isn't perfectly circular.

So, while Earth's orbit isn't perfectly circular, it's much closer to a circle than a highly elliptical orbit.