a) DIRBE all-sky map used as incident radiation field with surface brightnesses ranging from 0.08 to 12.6 MJy/sr. b)−d) Three all-sky maps in Galactic coordinates centered on the GC. The maps show the phase function-integrated surface brightness of ISRF radiation being completely scattered by a cell with dust at each sky location towards the observer. The maximal grain size of the dust size distribution is 0.25 a); 0.5 b); and 1 μm c); respectively. Local maxima arise near the Galactic plane (especially near the Galactic center and the anti-center) due to peaks in the phase function for forward and backward scattering.