Sign of the day-night asymmetry for solar neutrinos

A qualitative understanding of the day-night asymmetry for solar neutrinos is provided. The greater night flux in {nu}{sub e} is seen to be a consequence of the fact that the matter effect in the Sun and that in the Earth have the same sign. It is shown in the adiabatic approximation for the Sun and constant density for the Earth that, for all values of the mixing angle {theta}{sub V} between 0 and {pi}/2, the night flux of neutrinos is greater than the day flux. Only for small values of {theta}{sub V} where the adiabatic approximation badly fails does the sign of the day-night asymmetry reverse.