Thursday, August 1, 2013

1307.8218 (M. N. Vahia et al.)

Ancient eclipses and long-term drifts in the Earth - Moon system    [PDF]

M. N. Vahia, Saurabh Singh, Amit Seta, B. V. Subbarayappa
We investigate the anomalies in the Earth - Moon system using ancient eclipse data. We identify nine groups of anomalous eclipses between 400 and 1800 AD recorded in parts of India that should have completely missed the subcontinent as per NASA simulations (Espenak and Meeus, 2011). We show that the typical correction to the lunar location required to reconcile the anomalous eclipses is relatively small and consistent with the fluctuations in the length of day that are observed in recent periods. We then investigate the change in Earth's moment of inertia due to differential acceleration of land and water that can account for this discrepancy. We show that 80 percent of these discrepancies occur when the Moon is at declinations greater than 10 deg and closer to its major standstill of 28 deg while it spends 46 percent of the time in this region. We simulate the differential interaction of the Moon's gravity with landmass and water using finite element method to account for landmass and water mass. We show that the results of eclipse error are consistent with the estimate of a small differential acceleration when the Moon is over land at high latitudes. However, we encounter some examples where the results from simulations studies cannot explain the phenomena. Hence we propose that dT corrections have to be coupled with some other mechanism possibly a small vertical oscillation in the Moon's rotational plane with a period of the order of a few hundred years to achieve the required adjustment in the Eclipse maps.
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