An experiment to measure the instantaneous distance to the Moon

Abstract

We propose an experimental technique for determining the distance to the Moon. Our technique is based on measuring the change in angular size of the lunar disk due to the variation of the observer-Moon distance, as caused by the rotation of the Earth over several hours. Using this method we obtained a value of 3.46 × 105 km with a precision of 7%. Additionally, our technique allows for the determination of the Moon radius (1678 km ± 7%), and the instantaneous radial velocity with respect to the Earth (26.4 m/s ± 26%). A unique advantage of this method is that it is performed from a single location with a single observer, unlike the traditional parallax-based measurements that require at least two observers with a large separation distance.