  Day-night asymmetries in active-sterile solar neutrino oscillations are
discussed in the general $3+N_{s}$ mixing framework with three active and N_s
sterile neutrinos. Analytical expressions of the probability of neutrino flavor
transitions in the Earth in the perturbative approximation and in the slab
approximation are presented and the effects of active-sterile mixing and of the
CP-violating phases are discussed. The accuracy of the analytical
approximations and the properties of the day-night asymmetries are illustrated
numerically in the 3+1 neutrino mixing framework.
