Mizar, 88 light-years distant, is the middle star in the handle of the Big Dipper. It was the first binary star system to be imaged with a telescope. Spectroscopic observations show periodic Doppler shifts in the spectra of Mizar A and B, indicating that they are each binary stars. But they were too close to be directly imaged — until May 2, 1996, when the Navy Prototype Optical Interferometer (NPOI) produced the first image of Mizar A. That image had the highest angular resolution ever achieved in optical astronomy. Since then, the NPOI has observed Mizar A in 23 different positions over half the binary’s orbit. These images have been combined to make this movie. As a reference point, one component’s position has been fixed; in reality, the two stars are of comparable size and revolve about a common central position.
Mizar A movie
An optical interferometer records the dance steps of the two stars of Mizar A.