  Radial velocity perturbations induced by stellar surface inhomogeneities
including spots, plages and granules currently limit the detection of
Earth-twins using Doppler spectroscopy. Such stellar noise is poorly understood
for stars other than the Sun because their surface is unresolved. In
particular, the effects of stellar surface inhomogeneities on observed stellar
radial velocities are extremely difficult to characterize, and thus developing
optimal correction techniques to extract true stellar radial velocities is
extremely challenging. In this paper, we present preliminary results of a solar
telescope built to feed full-disk sunlight into the HARPS-N spectrograph, which
is in turn calibrated with an astro-comb. This setup enables long-term
observation of the Sun as a star with state-of-the-art sensitivity to radial
velocity changes. Over seven days of observing in 2014, we show an average
50\cms radial velocity rms over a few hours of observation. After correcting
observed radial velocities for spot and plage perturbations using full-disk
photometry of the Sun, we lower by a factor of two the weekly radial velocity
rms to 60\cms. The solar telescope is now entering routine operation, and will
observe the Sun every clear day for several hours. We will use these radial
velocities combined with data from solar satellites to improve our
understanding of stellar noise and develop optimal correction methods. If
successful, these new methods should enable the detection of Venus over the
next two to three years, thus demonstrating the possibility of detecting
Earth-twins around other solar-like stars using the radial velocity technique.
