An outbreak of brightness and storms occur on Mars when the Earth is between the Sun and Mars. The atmosphere and clouds can then be seen and photographed at short wavelengths by Earth-based telescopes equipped with a Wratten 47 filter. It happens that the blue screen of the filter suddenly begins to disappear and that the Martian surface becomes visible. We believe that the "Allais syzygy effect" may explain this phenomenon known as "blue clearing". The opposition would generate a "gravito-electromagnetic tension", which would spawn fluctuations in the gravitational potential of Mars. Assuming that the Martian gravity decreased slightly, a Stokes Raman scattering would manifest at intramolecular level of the Martian. Therefore, it is mainly the waves corresponding to the spectral regions yellow, orange or red that are diffused, what eliminates short wavelengths. We deduce that the size of the inhomogeneities resulting from thermal excitation turns out to be greater than the length of the light waves of blue or purple regions of the spectrum.