Astrometric Binary

Involve observing the more luminous star, and as it moves across the sky, rather than following a straight path, it demonstrates a back-and-forth "Wobbling" motion along its trajectory. This motion serves as an indication that the star is in orbit, allowing to infer the existence of a companion.

Two stars orbit about a common center of mass, which in turn moves across the sky. The fainter star is too faint to see, so we only see the brighter star, moving back and forth across the path of the center of mass.