a) Abedo ω (blue squares) and asymmetry factor, g, (green triangles) for standard dust defined in Sect. 3.1; it is used in all models of this paper. Points mark frequently used wavelengths, like UBVRI ...b) Standard dust produces in pencil beam observations the standard extinction curve ℰ_λ (red triangles). The black squares display the effective extinction curve assuming a Henyey-Greenstein phase function towards an unresolved shell source (see Fig. 2) with τ_V = 2 and other parameters as described in Sect. 5.2.1.