The Strange History of the Doppler Effect and Binary Stars

In 1842, German physicist Christian Doppler published an intriguing paper purporting that the peak colors of the members of binary star systems vary on the basis of the relative radial velocities of the sources and the terrestrial observer. His clever formula delineating the Doppler effect has become a key part of physics. The problem back in the 1840s was that the composition and spectra of stars was unknown, and not fully examined until later that century. Thus, ironically, the Doppler effect was not the key component of a full explanation of spectral variations in binaries. Luckily, however, as Ernst Mach and others would demonstrate, the effect applied beautifully to sound. Only later could it accurately be tested for starlight.