Relativistic effects from planetary and lunar observations of the XVIII–XX centuries

Abstract

Lunar and planetary observations of different types are discussed for the time span 1717–1982. The modern ranging observations and the historical ones (mainly transits of Mercury and Venus, solar eclipses and occultations of the inner planets by the Moon) are treated separately and some attempts to detect relativistic effects are carried out. From time delay observations linear combination ν = (2 + 2 γ-β) /3 of the parameters of the PPN formalism is evaluated: ν =0.997±0.003. Statistically significant estimate for the rate Ġ of changing of the gravitational constant G is found: Ġ/G=(4±0.8) · 10−11 /yr. (An alternative interpretation of this result due to Canuto et al. (1979) gives negative sign for Ġ). From transits of Mercury and Venus corrections to the adopted system of differences between the ephemeris (dynamic) and the atomic time scales and a correction to the Mercury's perihelion advance are deduced. With new ephemeris time scale it became possible to determine unambigiously lunar tidal deceleration ṅM making use of the historical lunar observations. The derived value ṅM = (−22.2 ± 0.8)′′/cy2 is in good agreement with reported lunar laser results. By comparing the estimates ṅM obtained by the two methods the rate Ġ has also been evaluated: Ġ/G=(0.5+0.5)·10−11/yr. The origin of the disagreement with the radar based result for Ġ is not yet clear. All the conclusions were checked by making use of different planetary and lunar theories and appear to be practically theory-independent.