It could be. But if the names of the other planets aren't familiar to you, your world could be part of a different system. [Given that she didn't react to the word "Earth," there's a good chance that it's the latter.] Orbit: the curved path of a celestial object or spacecraft around a star, planet, or moon, especially a periodic elliptical revolution.

Have you ever heard of the theory of gravity? [Fugo picks up one of the stones that they've gathered.] Gravity is the force that brings objects together-- [He releases the stone. It, of course, falls down to the ground.] Like this. Gravity pulled the stone back to the ground. It's a little more complicated than this-- but one way to think about it is that the more massive an object is, the stronger force of gravity it has.

An orbit is a sort of perfect balance between two large celestial bodies. [Fugo holds up his fist, again to represent the sun, and another of the stones; as he speaks, he uses his other hand to illustrate what he's trying to explain.] The larger celestial body has a much stronger force of gravity than the smaller celestial body. When the smaller one passes by it, it gets "caught" by the gravity and pulled in. If the smaller celestial body has strong enough inertia-- forward momentum-- it becomes locked in a cyclic tug-of-war as it continues to try to move forward, but the larger body's gravity pulls it back in towards it.

[He pauses, both in his lecture and demonstration, finally realizing that all of that was... probably a bit much all at once.]

Are you following me? If there's something you don't understand, you can stop me and I'll try to explain it better.