This is due to Kepler's Laws of Planetary Motion, specifically the first law, which states:
* The orbit of every planet is an ellipse with the Sun at one of the two foci.
This means that a planet's path around the Sun is not a perfect circle, but rather a slightly elongated oval shape. While some orbits are closer to circular than others, they are all technically ellipses.
Here's why this matters:
* The Sun's gravity is not constant: It's strongest when a planet is closest to it and weaker when it's furthest away.
* Conservation of energy: As a planet moves closer to the Sun, it gains speed, and as it moves further away, it slows down. This constant change in speed and distance results in the elliptical path.
While some planets may have very nearly circular orbits, all planets follow an elliptical path, regardless of their size or distance from their star.
