We reexamine the conventional physical description of the neutrino evolution inside the Sun. We point out that the traditional resonance condition has physical meaning only in the limit of small values of the neutrino mixing angle, θ ≪ 1. For large values of θ, the resonance condition specifies neither the point of the maximal violation of adiabaticity in the nonadiabatic case, nor the point where the flavor conversion occurs at the maximal rate in the adiabatic case. The corresponding correct conditions, valid for all values of θ including θ > π/4, are presented. An adiabaticity condition valid for all values of θ is also described. The results of accurate numerical computations of the level jumping probability in the Sun are presented. These calculations cover a wide range of ∆m 2 , from the vacuum oscillation region to the region where the standard exponential approximation is good. A convenient empirical parametrization of these results in terms of elementary functions is given. The matter effects in the socalled "quasi-vacuum oscillation regime" are discussed. Finally, it is shown how the known analytical results for the exponential,