Measured magnitude across the umbra edge with HARPS at 5500 Å. Crosses and diamonds stand for A and B fiber, respectively. The horizontal error bars are 2σ = 20 arcsec long and represent the typical pointing error of the telescope. Vertically, the 2σ error bars are the magnitude errors evaluated from the S/N of the spectra at that wavelength and the evaluated error in the local Moon albedo. The solid line is the model from Eq. (4) fitted through the data. The vertical dotted line marks our definition of the umbra edge. See Sect. 7.3 for details.