The newly discovered Alcor B orbits its larger sibling Alcor and was caught in the act with an innovative technique called "common parallactic motion" by members of Project 1640, an international collaborative team that includes astrophysicists at the American Museum of Natural History, the University of Cambridge's Institute of Astronomy, the California Institute of Technology, and NASA's Jet Propulsion Laboratory.
Four hundred years ago, he realized that if Copernicus was right-that the Earth orbits the Sun-they could show it by observing the "parallactic motion" of the nearest stars.
Parallactic motion is the way nearby stars appear to move in an annual, repeatable pattern relative to much more distant stars, simply because the observer on Earth is circling the Sun and sees these stars from different places over the year.