How Do Circular Gears Create Elliptical Motion?

orbital mechanics an like kepler's second law works. When the moon is far away from the earth, it's going slower relative to us. But when it's closer to the earth,. it's going faster, right? That's how orbital mechanics work. They figured that out way back in the day and created an ingenious ellipsoidal gearing mechanism. It's basically a circular gear inside of a gear.