COSMIC ACCELERATION OF EARTH AND THE MOON BY DARK-MATTER

In order to test the hypothesis that the gravitational interaction bet ween our Galaxy's dark matter and the ordinary matter in Earth and the Moon might not fulfill the equivalence principle (universality of fre e fall), we consider the pertinent perturbation of the lunar orbit-a s idereal month period range oscillation resulting from a spatially fixe d polarization of the orbit. Lunar laser ranging (LLR) data can measur e this sidereal perturbation to an accuracy equal to or better than it s existing measurement of the synodic month period range oscillation a mplitude (+/-3 cm) which has been used for testing whether Earth and t he Moon accelerate at equal rates toward the Sun. Because of the slow precession rate of the Moon's perigree (8.9 yr period), the lunar orbi t is particularly sensitive to a cosmic acceleration; the LLR fit of t he orbit places an upper limit of 10(-13) cm s(-2) for any cosmic diff erential acceleration between Earth (Fe) and the Moon (silicates). Thi s is 10(-5) of the total galactic acceleration of the solar system, of which, it has been suggested, a large portion is produced by dark mat ter.