  We compute the interaction of a sodium vapor with a static magnetic field
ranging from 0 up to 1 Tesla, which allows to obtain the behavior of all Zeeman
transitions as a function of the magnetic field for any polarization of
incident laser radiation: $\pi, \sigma^\pm$. We use these results combined with
a Fabry-P\'erot microcavity model to describe the transmitted and reflected
signal of a sodium vapor confined in a nanometric-thin cell. This allows us to
present for the first time high resolution absorption spectra, and provide a
complete description of the Zeeman transitions, along with some important
peculiarities such as the appearance of guiding transitions and
magnetically-induced circular dichroism. The obtained theoretical results can
be used in the upcoming experiments with sodium vapor nanocells.
