A proof of the constancy of the velocity of light

In that distant time the postulate «A proof of the constancy of the velocity of light» directly confirmed only by astronomical observations of double stars. The idea of the Dutch astronomer Willem de Sitter, if the speed of light depends on the velocity of the source, the trajectory of motion of binary stars would have to be qualitatively different from those observed (consistent with celestial mechanics). Here you can find examples and formulas for calculating the speed of light.