How Mercury orbits the sun
You may have noticed that the sun is not in the center of the orbit of Mercury. It is offset, making the orbit an ellipse. All the planets orbits are ellipses but Mercury’s is most obvious. Note that the stones at the top of the orbit are farther apart than at the bottom. This is because as Mercury gets closer to the sun it moves faster so the stones have to be farther apart to represent four days of travel. As the planet falls toward the bottom it slows down so four days is a shorter distance.