Empirical Earth Rotation Model: a Consistent Way to Evaluate Earth Orientation Parameters
It is customary to perform analysis of the Earth’s rotation in two steps: first, to present results of estimation of the Earth orientation parameters in the form of time series based on a simplified model of variations of the Earth’s rotation for a short period of time, and then to process this time series of adjustmentsby applying smoothing, re-sampling and other numerical algorithms. This approach suffers from self-inconsistency: the total set of Earth orientation parameters depends on a subjective choice of the apriori Earth orientation model, crosscorrelations between points of the time series are lost, and results of an operational analysis per se have a limited use for end users. Here, an alternative approach of direct estimation of the coefficients of expansion of Euler angle perturbations into basis functions is developed. These coefficients describe the Earth’s rotation over the entire period of observations and are evaluated simultaneously with stationpositions, source coordinates and other parameters in a single LSQ solution. In the framework of this approach considerably larger errors in apriori EOP model are tolerated. This approachgives a significant conceptual simplification of representation and estimation of the Earth’s rotation.
History of Astronomy
IN this small volume Prof. Forbes describes the evolution of astronomical knowledge under three periods—the geometrical, the dynamical, and the physical. In addition, in book iii. he also describes the evolution of the instruments which have enabled astronomers of all ages to contribute to the store of knowledge on which our present-day astronomy is based.History of Astronomy.By Prof. G. Forbes Pp. ix + 154; illustrated. (London: Watts and Co., 1909.) Price 1s. net.
A new nutation series for a more realistic model earth
SUMMARY 
 
The frequency-dependent correction coefficients with respect to the forced nutations of a rigid earth are computed using the complex scalar gravitational-motion equations for an earth model with an anelastic mantle. Oceanic loads and tidal currents enter the model via outer boundary conditions. The ellipticity of the core-mantle boundary and the dynamical ellipticity are adjusted to observations. This requires the behaviour inside the model earth to be regarded as non-hydrostatic. Some relevant equations for the evaluation of boundary conditions and some terms in the equations of motion are expanded to second order in ellipticity. The computation of the equipotential-surface ellipticity profile is carried to second order as well. These second-order expansions lead to increased accuracy of the results in general. Moreover, one achieves a better reliability for the integration at frequencies close to a resonance. This allows the integration of the equations of motion at any relevant nutation period without the need for a normal-mode expansion. A complete new nutation series for a realistic model earth is presented.