Isaac Newton explained that a planet moves through an elliptical orbit due to its gravitational attraction to the sun and its own inertia.

Here's why:

* Gravity: The sun's gravitational pull constantly pulls the planet towards it. This force is what keeps the planet from flying off into space.

* Inertia: Inertia is the tendency of an object to resist changes in its motion. If the planet were only influenced by gravity, it would fall directly into the sun. However, the planet's inertia causes it to move forward, creating a balance with gravity.

The interplay of these two forces:

* At the point closest to the sun (perihelion), the planet's speed is at its fastest. The pull of gravity is stronger, but the planet's forward momentum is high.

* At the point farthest from the sun (aphelion), the planet's speed is at its slowest. Gravity is weaker, and the planet's forward momentum has decreased.

This constant interplay of gravity and inertia creates the elliptical path of a planet.