  It is shown that the Sun can become partially transparent to high energy
photons in the presence of a pseudo-scalar. In particular, if the axion
interpretation of the PVLAS result were true then up to 2% of GeV energy gamma
rays might pass through the Sun, while an even stronger effect is expected for
some axion parameters. We discuss the possibilities of observing this effect.
Present data are limited to the observation of the solar occultation of 3C 279
by EGRET in 1991; 98% C.L. detection of a non-zero flux of gamma rays passing
through the Sun is not yet conclusive. Since the same occultation happens every
October, future experiments, e.g. GLAST, are expected to have better
sensitivity.
