  Gravitational microlensing is a new technique for studying the surfaces of
distant stars. A point mass lens, usually a low-mass star from the disk, will
typically resolve the surface of a red giant in the Galactic bulge, as well as
amplify its brightness by a factor of 10 or more. Such events are now detected
in real time and can be followed up with precision photometry and spectroscopy.
  The motivation for stellar imaging via microlensing lies in its unique
ability to provide center-to-limb variation of spectral diagnostic lines. Such
variation maps into a variation with depth in the stellar atmosphere - a unique
and very valuable constraint for modeling the structure of red giants'
atmospheres. We illustrate the technique on a recent successful observational
campaign and discuss the implications for current stellar models.
