Shining light through the Sun by axions

I show that the Sun can become partially transparent to high energy photons in the presence of a pseudo-scalar. I 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 to the discussed effect.