The experimental Brillouin spectra of light scattering on supersonic gas flows are presented. The results of numerical calculations on the base of a kinetic model given are in good accordance with the experimental data. The influence of a finite size and shape of an aperture on spectra contours is investigated. It was shown, that the optimal one to achieve maximal luminosity is the cross of a hyperbola and a parabola, similar to the shape of eye.