Dynamics of the Earth-Moon system

Abstract

Lunar laser ranging (LLR) has been used to determine the precise orientation of the Earth since the early-1970's. Two observatories currently range with 2.5 centimeter accuracy to a constellation of four retroreflector targets. The quality and the 23 year span of the lunar data permit the determination of the constant of precession to an accuracy of 0.5 mas yr −1. The 18.6 year and 9 year nutation terms can be well separated from the precession constant and determined at the milliarcsecond level. The extreme altitude of the Moon, as an Earth satellite, prevents the stochastic effects of atmospheric drag. This allows estimation of the local components of Earth rotation (UTO, Df) to an accuracy of 2.5 milliarcseconds from as little as 1.5 hours of lunar data, with higher accuracies for longer spans of data. This near real time capability makes LLR a strong technique for the investigation of diurnal, and even sub-diurnal, variations in Earth rotation. The secular increase in the mean distance between the Earth and Moon is observed with an accuracy of 0.15 cm yr −1. LLR observations permit the determination of the obliquity of the ecliptic and the equinox with an accuracy of a few milliseconds of arc. The mass of the Earth-Moon system has been estimated from the lunar ranges to one part in 100 million.