The (optically) dark side of the Moon is also X-ray dark, casting a distinct X-ray shadow of the diffuse X-ray background (DXBG). Thus we have performed the first unambiguously successful shadowing experiment of the DXBG, and shown that the, by far, dominant background component in the ROSAT PSPC arises from beyond the Moon as celestial X-rays, and not from events produced in the immediate vicinity of the satellite. A careful analysis of the observed signal from the dark moon shows it to be ~ 30 times larger than expected from pure particle events and earth-backscattered solar X-ray radiation. Therefore, the dark side of the Moon also emits soft X-ray radiation at the level of about 1% of the bright side; it has been suggested that this excess intensity is caused by Bremsstrahlung from supra-thermal electrons hitting the lunar surface.