The laser frequency comb in action

This picture illustrates part of a spectrum of a star obtained using the HARPS instrument on the ESO 3.6-metre telescope at the La Silla Observatory in Chile. The lines are the light from the star spread out in great detail into its component colours. The dark gaps in the lines are absorption features from different elements in the star. The regularly spaced bright spots just above the lines are the spectrum of the laser frequency comb that is used for comparison. The very stable nature and regular spacing of the frequency comb make it an ideal comparison, allowing the detection of minute shifts in the star’s spectrum that are induced by the motion of orbiting planets. Note that in this image, the colour range is for illustrative purposes only, as the real changes are much more subtle.