The FGS has been used (Lattanzi et al. 1997) to determine the angular diameters of non-point sources. The example given in Figure 3.5, Mira-type variable with a resolved circumstellar disk
shows the Transfer Function of a Mira-type variable superposed on the S-Curve of a point source (both observed with FGS3). The extended source - a disk of 78
mas - is clearly distinguishable from a point source. In addition to stellar discs, other objects which might be (or have been) resolved by the FGS include galactic nuclei, asteroids, and planetary moons.