It doesn't; that language is garbled. It's the velocity of the star they're observing that changes by several cm/s. This translates to a Doppler shift in the st

It doesn't; that language is garbled. It's the velocity of the star they're observing that changes by several cm/s. This translates to a Doppler shift in the starlight being detected: a change in its frequency and wavelength. see also https://en.wikipedia.org/wiki/Doppler_spectroscopy https://en.wikipedia.org/wiki/Doppler_spectroscopy