<p>Finding an Earth–Sun analogue is one of the longest-standing goals in astronomy. The detection of such a system using the radial velocity (RV) technique is highly challenging, and would require coordinated advances in astronomical telescopes, fibre optics, precision spectrographs, large-format detector arrays and data processing. Measurements at the necessary 10⁻¹⁰ level over multiyear periods would also require a highly precise calibrator. Here we explore simple and robust white-light-illuminated Fabry–Pérot (FP) etalons as spectral calibrators for precise RV measurements. We track the frequencies of up to 13,000 FP modes against laser frequency combs at two state-of-the-art spectrographs and trace unexpected chromatic variations of the modes to subpicometre changes in the dielectric layers of the broad-bandwidth FP mirrors, corresponding to a RV precision at the centimetres per second level. These results represent critical progress in precision RV measurements in two ways—they validate FP etalons as a more powerful stand-alone calibration tool and demonstrate the capability of laser frequency combs to extend RV measurement precision at the centimetres per second level over periods approaching a year. These advances highlight a path to achieving spectroscopic calibration at levels that will be critical for finding Earths like our own.</p>