Viewed from ten light-years away, the sun's side-to-side astrometric wobble due to the effect of the earth is just one millionth of an arcsecond, or a twentieth of the tiniest angle that the Keck will be able to measure.
Marcy and a team that includes Paul Butler of the Anglo-Australian Observatory are using the telescope to scan more than 400 stars for the characteristic "wobble" caused by the gravitational effect of planets on stars.