How did the binary star shift happen?
“Spectroscopic binaries” are stars orbiting each other which are so close together that they cannot be resolved as separate stars optically. However we can tell that they are two stars rather than one, because the pattern of spectral lines shifts back and forth with time. As one of the stars moves around its orbit, sometimes it’s moving towards us (and the spectrum will be blueshifted) and sometimes it’s moving away from us (and the spectrum will be redshifted). If we see this sloshing back and forth with time, we know that the star has to be orbiting another star, and so it must be a binary. In the Mizar case, there are actually four stars, comprising two systems of two spectroscopic binaries each. The two systems are a “visual binary” system, meaning that it is indeed possible to resolve them as separate systems with a telescope. The spectroscopic binaries are binary stars that are orbiting each other too closely to resolve with a telescope- but we know that they are binaries by
