Orbital Wobble

Snapshot 1: In some systems, the center of mass, which is also known as the barycenter, is found well inside the larger body. This occurs, for instance, if the larger body has a considerably larger mass than the smaller one. As a result, the larger body wobbles slightly as the two bodies revolve around the barycenter.

Snapshot 2: If the two bodies are closer in mass, with the barycenter still inside the larger body, the wobble will be more pronounced.

Snapshot 3: If the two bodies have roughly the same mass, the bodies rotate around the barycenter without appearing to wobble.