Universal time, lunar tidal deceleration and relativistic effects from observations of transits, eclipses and occultations in the XVIII-XX centuries
Astronomy and Astrophysics, 145, 90-96 (1985)
Keywords: planetary and lunar theory, relativity effects, lunar tidal deceleration
About the paper Full textAbstract
Lunar and planetary observations for the time span 1717-1973 (transits of Mercury and Venus, solar eclipses, occultations of Venus, Mars and Mdebaran) are discussed. Two modern planetary and lunar theories are used, the first theory being constructed at the Institute for Theoretical Astronomy (Lehingrad) and the other one - at the Bureau des Longitude (Paris). It is shown that the adopted system of differences between the ephemeris (dynamic) and universal time requires the correction (-12S ± 1S3)/cy before 1960. With this new UT time scale the evaluation bf the observed secular motions of the perigee and the node of Mercury is made and the consistency with the relativistic values is confirmed within 1" limits. From transits of Mercury a statistical significant value of the secular decrease of the solar radius is found. However, there is an evidence indicating that this effect is entirely due to a change of the observational conditions after 1940 and has no real physical basis. For the parameter nM of the lunar deceleration the estimations nM = (-22".9 ± 0".8)/cy2 or nM = (-22".2 ± 0".8)cy2 (depending on the theory used) are obtained. These estimates are in agreement with nM derived in atomic time scale from the analysis of lunar laser ranging. Such an agreement does not support the hypotheses of the secular decrease of the gravitational constant.