Number 127 (Story #1), May 5, 1993 by Phillip F. Schewe and Ben Stein THE OPPOSITION EFFECT OF THE MOON , a phenomenon known for more than a century in which the Moon's brightness goes up markedly as it becomes full (goes into opposition), can now be attributed to coherent backscattering. That is, incoming sunlight scatters repeatedly from lunar particles smaller than the light's wavelength and builds up prominently in the backward direction. The opposition effect, studied by scientists at the University of Pittsburgh and JPL using lunar rock samples, applies also to other reflective objects in the solar system such as Saturn's rings. (Science, 23 April.)