Binary system telescope or binoculars. Eclipsing binaries are where the objects' orbits are at an angle that when one passes in front of the other it causes an eclipse, as seen from Earth. Astrometric binaries are objects that seem to move around nothing as their companion object cannot be identified, it can only be inferred. The companion object may not be bright enough or may be hidden in the glare from the primary object. A related classification though not a binary system is Optical binary which refers to objects that are so close together in the sky that they appear to be
Binary asteroid Binary asteroid A binary asteroid is a system of two asteroids orbiting their common barycenter. The binary nature of 243 Ida was discovered when the Galileo spacecraft flew by the asteroid in 1993. Since then numerous binary asteroids and several triple asteroids have been detected. The mass ratio of the two components – called the "primary" and "secondary" of a binary system – is an important characteristic. Most binary asteroids have a large mass ratio, i.e. a relatively small satellite in orbit around the main component. Systems with a small minor-planet moon – also called "companion" or simply "satellite" –