Radial velocity observations of the sun at night

We have measured the Doppler shift of the solar spectrum for 5 yr to help demonstrate our ability to detect planets orbiting other stars. The sunlit surface of the Moon provides nighttime access to the solar spectrum integrated over the solar disk, as if the Sun were being observed at a stellar distance. The standard deviation of our 486 lunar observations spanning 4.9 yr is ±7.8 m s −1 , consistent with our short-term internal precision and external calibration accuracy. Long-term periodic errors in the instrument are ±4 m s −1