Stars don't have uniform surfaces, and they rotate. Can you see the orientation of the star in a single spectrum? Of course the answer is no: You don't have a coordinate system! But if you have some previous spectra of the star, can you establish a rotation period and define an angular coordinate system, and then follow that by taking a new spectrum and saying where the star is in its rotational phase? It looks like the answer to this question might be yes, based on experiments that Lily Zhao (Flatiron) is doing. Of course we don't really care about the stellar orientation. What we care about is capturing or correcting the artificial radial-velocity signals introduces to the data from the rotating, non-uniform surface.
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