Observation of terrestrial orbital motion using the cosmic-ray Compton–Getting effect

Abstract

Using underground observations, we have found a small diurnal amplitude modulation of the cosmic-ray muon intensity which agrees in amplitude and phase with a first-order relativistic effect due to the Earth's motion, as discussed by Compton and Getting more than fifty years ago. The parent particles are sufficiently rigid (∼1.5TeV/c) that solar and geomagnetic effects should be minor. The muon flux deep underground is relatively insensitive to near-surface meteorological effects, and temperature effects at production height would produce intensity variations nearly out of phase with the observed effect. Analysis of the arrival times of 5 × 108 muons during a period of 5.4 yr yields a fractional amplitude variation of 2.5+0.7−0.6× 10−4, with a maximum near dawn, at 08:18 ± 1.0 h local mean solar time (LT). The expected amplitude is 3.40 × 10−4, with the maximum at 06:00 LT.