While it was initially thought that planets moved in perfect circles around the Sun, we now know that their orbits are actually elliptical.

Here's why:

* Kepler's Laws of Planetary Motion: Johannes Kepler, a German astronomer, observed the planets and formulated three laws of planetary motion. His first law states that planets move in elliptical orbits with the Sun at one focus of the ellipse.

* Gravity and Ellipses: Gravity is the force that keeps planets in orbit. The force of gravity is not constant at all points in the orbit, which leads to the elliptical shape.

* Speed Variation: Planets travel faster when they are closer to the Sun and slower when they are farther away. This variation in speed is another indication of an elliptical orbit.

In summary:

While circles are a simple and easy-to-understand shape, they don't accurately represent the complex motion of planets. Ellipses are the true shape of planetary orbits, reflecting the influence of gravity and the varying speed of planets in their paths around the Sun.