Chapter 12 The position and Doppler shift of a star orbiting its common center of mass with a planet

When the planet is moving away from us and the star is approaching us, the spectral lines of the star are blue shifted. When the planet is approaching us and the star is moving away from us, the spectral lines of the star are red shifted. The position of the center of mass is marked with an x. Both the shift in position and the Doppler shift of the spectral lines are very greatly exaggerated.