A.H. Andrei, A. Fienga, M. Assafin, J.L. Penna, M. Schulteis, D.N. da Silva Neto, R. Vieira Martins

IMCCE (on leave from home institution) & GEA/ON/OV

The GAIA extragalactic reference frame (GERF) will be formed by about 500,000 quasars, up to magnitude G=20, defined to typical precision of 50$\mu$as. We present a restricted representation of the GERF, based on the Veron-Cetty & Veron (2003, A&A) list of 48921 quasars. This representation brings the original list to a fully coherent placement on the ICRS. The sources have been collected from dense catalogs, such as the USNO B1.0, which is complete to V=20. Around each of them, small fields of size 6arcmin were detailed, in which were picked up B1.0 stars and their corresponding positions from catalogs extending the HCRF to dimmer magnitudes. The UCAC2 and the 2MASS acted as the astrometric reference catalogs. Taking as paradigm the B1.0 positions corrected by the UCAC2, a reference frame containing 37513 quasars is obtained, aligned to 1mas with the ICRF. The optical minus radio standard deviation is at 118mas, much smaller therefore than the nominal 200mas B1.0 accuracy (the o-r standard deviation is above 300mas for the original V&V entries). The extragalactic reference frame so obtained enables to gather insights on the GERF and provides an useful frame for all purpose observations.

E. F. Arias, B. Guinot

Bureau International des Poids et Mesures

The system of Coordinated Universal Time, UTC, was initially conceived at the beginning of the 1960?s as a means of improving the dissemination of Universal Time, UT1, and to make available the stable frequency of atomic standards in a single time signal emission. It gradually evolved by relaxing the tolerance on UT1 and in 1971 reached the form we know to-day. This evolution is described. In spite of its success, borne out by 33 years of existence, the present system suffers increasingly from the inconvenience of leap seconds. These notes bring together some astronomical elements that should be kept in mind in any proposed revision of the UTC system: the modern definition of UT1, its long term irregularities. We focus on the possibility of prediction of the difference UT1 ? International Atomic Time within +/- 1 second, because this is the tolerance of UTC ? UT1. Clearly, at such a level of precision, annual ephemeredes using TAI (or any other uniform time) as argument can be published well in advance for those who do not want to apply corrections. Finally we give our views on a new system of time dissemination.

Elisa Felicitas Arias, S?bastien Bouquillon

Bureau International des Poids et Mesures

The axes of the International Celestial Reference System (ICRS) are realized by the J2000 equatorial coordinates of 212 extragalactic radio sources qualified as the ? defining ? objects of the International Celestial Reference Frame (ICRF). They have been selected by applying quality criteria to VLBI observations between 1975-1995. Feissel-Vernier (A&A 403, 105, 2003) proposed another list of selected sources based on an analysis of time series of radio source coordinates ; in this case the observations included in the analysis are in the period 1989-2002. As a contribution to the maintenance and the extension of the ICRF, we have studied and compared the representations of the ICRS by the two sets of selected sources.

Y. Barkin

Sternberg Astronomical Institute, Moscow

In cycle author?s papers in 1976-1987 years the Poincare?s theory of periodic solutions has been developed and applied for systematic studies of resonant rotations of the Moon, Mercury and Venus. 1. The new classes of the plane (Barkin, 1976, 1979a) and spatial (Barkin, 1977a, 1979c) periodic translatory-rotatary motion of the non-spherical body in gravitational field of the central body have been found. A. A theoretical value of the equatorial ellipticity of Mercury tensor of inertia has been evaluated (Barkin, 1976). B. The amplitudes of Mercury librations with periods 88 and 44 days were found and evaluated (Barkin, 1979a). C. The period of resonant Mercury libration in longitude was evaluated as 18-26 years (Barkin, 1983). 2. Existance, stability, neibourhood of new class of periodic solutions have been investigated in the problem about rotational motion of the non-spherical rigid satellite on precessing circular orbit. A. Poincare?s generating solutions have interpretated and illustrated as generalized Cassini?s laws (Barkin, 1978b). B. Periodic librations of the Moon were described by the corresponding Poincare?s periodic solution of the problem and main dynamical effects have been determined (Barkin, 1983). C. Periods of resonant librations of the Moon in vicinity of found periodic solution have been described analytically and evaluated as (in years): 2.88, 75.20, 24.68 (Barkin, 1983). 3. Special class of periodic Poincare?s solutions of the first kind was found and studied in the plane problem of the three gravitating bodies (Venus is a non-spherical rigid body and the Sun and the Earth are considered as material points). A. A generating periodic solution describing observed resonance in the Venus translatory-rotary motion has been found (Barkin, 1987a). B. The main periodic librations of Venus have been determined. C. Stability of periodic Venus motion has been studied. D. The period of Venus resonant libration in longitude has been evaluated. E. Small constant deviation of the equatorial principal axis of inertia of Venus in longitude has been predicted. Generalization of Poincare?s theory of periodic solutions has been developed for some types of degenerating Hamiltonian systems containing one or a few small parameters. Conditions of existence, of stability of periodic solutions have been obtained. Algorithms of constructing of periodic solutions in form trigonometric series and solutions in vicinity of discussed periodic solutions have been developed (Barkin, 1979b; Barkin, Pankratov, 1987a-c). Detailed description and illustrations of the resonant phenomena in the motion of the Moon, Mercury and Venus on the base of present observed data are given in report.

Yu.V. Barkin, J.M. Ferrandiz

Alicante University, Spain; Sternberg Astronomical Institute, Moscow

The theory of the unperturbed and perturbed rotation of deformable celestial body (the Earth) is developed on the base of equations in angle-action variables. This unperturbed motion describes the rotation of an isolated celestial body weakly deformed by its own rotation. On the base of equations in Andoyer variables describing rotational motion of the celestial bodies with a changeable in the time tensor of inertia the problem is reduced to the classical Euler-Poinsot problem for a rigid body, but with another set of constant moments of inertia. The unperturbed motion describes Chandler?s pole motion and we have called it as the Chandler or Euler-Chandler motion. The solution of the Chandler problem (Andoyer?s variables, components of angular velocity w.r.t to the body and space reference systems, direction cosines and their different functions) is presented in elliptical and theta-functions, and in the form of Fourier series in the angle-action variables. Perturbations of the first order in the Earth rotation caused by gravitational attraction of the Moon and the Sun are presented in the form of trigonometric series with respect to multiples of angle variables and arguments of lunar orbital motion. Coefficients of these series are presented in the terms of elliptical integrals, elliptical and hyperbolic functions of initial values of action variables and some elastic parameter k. Properties of unperturbed rotation also depend from mentioned parameters. It has let us to study a contribution of the elastic properties of the Earth mantle in observed and possible new phenomena in the Earth rotation. In report we discuss the following phenomena in unperturbed motion. 1. The known phenomenon of a distinction of Euler and Chandler periods is confirmed by unperturbed theory (433.2 and 304.4 days). 2. A new phenomenon of a distinction of eccentricities of Euler and Chandler pole trajectories (corresponding geometrical eccentricities are 0.00328 and 0.00462). 3. Non-uniformity of Chandler motion. 4. Small variation of the angular velocity of the Earth with a half Chandler period. 5. Chandler changes of projection of angular momentum of the Earth on its polar axis of inertia. 6. Extreme values of the angle between the angular momentum vector and polar axis of inertia of the Earth in unperturbed motion. 7. Extreme values of the angle between vectors of the angular momentum and angular velocity. 8. Extreme values of the angle between the angular momentum vector and polar axis of inertia of the Earth. 9. Variations of the moment of inertia of the Earth about rotation axis. For perturbed Earth rotation the following phenomena were discussed. 1. Contribution of gravitational attraction of the Moon and the Sun to mean angular velocity of the Earth and in Chandler period. 2. Influence elasticity on the value of constant of precession. 3. Contribution of elastic properties of the mantle in values of amplitudes of first order perturbations in angle-action variables. The Barkin?s work was supported by Spanish grant SAB2000-0235 and RFBR grant 02-05-64176.

S. Bolotin

Main Astronomical Observatory NASU, Kiev, Ukraine

A set of VLBI observations carried out since 1992 till August 2004 were analyzed to construct a Celestial Reference Frame. Data processing was conducted according to IERS Conventions 2003 with the software SteelBreeze. Coordinates of stations and Earth Rotation Parameters were fixed and their values were taken as a priori from the VTRF2003 and EOP(IERS) C 04 solutions. In total, the obtained extension of Celestial Reference Frame consists of positions of 2028 radio sources.

O. Bolotina

Main Astronomical Observatory NASU, Kiev, Ukraine

In the paper an upgraded Ukrainian Center of determination of the Earth Orientation Parameters (UCEOP) is presented. The history and purposes of a creation of the UCEOP are given. Current structure of the Ukrainian Center of determination of the Earth Orientation parameters is presented. Ukrainian Space Geodynamics Networks as well as software, models and methods which are used in the UCEOP Analysis Centers for data analysis are described.

G. Bourda

Observatoire de Paris

The ?Descartes-Nutation? Project is devoted to the ?understanding of the next decimal of precession-nutation, from the theoretical point of view as well as from the observational point of view?. In this framework, we made a proposal in order to contribute to the study of (i) the dynamical flattening of the Earth, (ii) the coupling effects of the lunisolar forcing, (iii) the effect of the geophysical fluids on the EOP and (iv) the Nutation observations.We investigate further the links between Earth Orientation and Gravity Field Variations. Indeed, the masses distributions inside the Earth govern the behaviour of the rotation axis in space (precession-nutation) and in the Earth (polar motion), as well as the Earth rotation rate (or equivalently, length of the day). These distributions of masses can be measured by space owing to artificial satellites, the orbitography of which provides the Earth gravity field determination. Then, the temporal variations of the Earth gravity field can be related to the variations of the Earth Orientation Parameters (EOP) (with the Inertia Tensor). Nowadays, the Earth orientation measurements in space, obtained with Very Long Baseline Interferometry (VLBI), have a precision better than the milliarcsecond level. It is then necessary to consider all the geophysical sources that can improve the models precision. The goal of my PhD Thesis was to use the Earth gravity field measurements, as well as its variations, as a tool to improve the Earth orientation modelisation. We present here the results obtained as well as various proposals to extend these investigations (numerical studies, the use of J2 geophysical series, integration of GRACE data ?).

A. Brzezinski

Space Research Centre, Polish Academy of Sciences, Warsaw, Poland

The non-tidal variability in the ocean is expcted to have a significant influence on Earth rotation over a broad range of frequencies. Brzezinski et al. (2004; paper presented at the EGU GA in Nice) used a new 7.5-year time series of ocean angular momentum with high temporal resolution(sampling interval 1 hour) calculated from a barotropic numerical model, to study the influence of wind- and pressure-driven ocean signals on nutation. Here we used the same excitation series to estimate the non-tidal oceanic contribution to diurnal and semidiurnal polar motion. Firstwe compute parameters of the harmonic model in the spectral bands of interest: prograde diurnal, retrograde and prograde semidiurnal. Then, we remove the harmonic models and consider separately the irregular remainders. At each stage the oceanic excitation is compared to the atmospheric contributions derived from the atmospheric angular momentumdata and to other known influences. An important question discussed here is how the dynamical response of the ocean to the atmospheric forcing differs at diurnal and semidiurnal frequencies from the two simple models applied so far, one assuming the "inverted barometer" response and the other one assuming the "rigid ocean" response. We also addres the problem of reliability of the excitation series at diurnal and semidiurnal frequencies.

J.I.B Camargo, G. Daigne, C. Ducourant, P. Charlot

Observatoire de Bordeaux - OASU/L3AB

High-quality astrometry and photometry in the J, H and Ksbands were obtained for 30 southern ICRF quasars with magnitudes 11.5 < Ks < 17.5. Observations were carried out with the ESO NTT/SOFI at la Silla, Chile. While the internal astrometric precision of these measurements is better than 10 mas, the actual accuracy is limited by thestatistical errors of the reference catalogue (UCAC2).Mosaics of overlapping images around fourteen quasar fields were made in order to reduce such errors. The rms of the differences between the observed and the ICRF positionsis then better than 30 mas. The magnitude precision is 0.04 mags for the three bands. One of the objectives of this project is to provide a selection of candidates to the optical/near-IR extension of the ICRF.

N. Capitaine

Observatoire de Paris, Syrte

This paper reviews a number of effects that must be taken into account in developing improved expressions for precession and nutation of the Earth in order that they are dynamically consistent and compliant with up to date models for the ecliptic and for non-rigidity of the Earth. We report on the effects which were considered in the development of the P03 and parameterized P04 solutions of Capitaine et al. (2003, 2004) for the precession of the equator. This includes effects of the ecliptic model, of the precession rates values and of some parameters of non-rigidity as the J2 rate effect (Bourda & Capitaine 2004). This also includes the dependence of the estimated precession rate in longitude on the obliquity of the conventional ecliptic which is used and on the procedure for taking into account the frame biases between the mean equatorial frame and the Geocentric Celestial Reference System (GCRS). The theoretical differences between various solutions are evaluated and the dynamical consistency of precession solutions is compared to that of IAU 2000. We also review a number of effects in nutation such as those similar to the above ones for precession and the influence of the variations in Earth rotation that was recently clarified (Lambert & Capitaine 2004). Some recommendations are given regarding the form of improved precession-nutation expressions and the best appropriate parameters to be fitted to observations.

N. Capitaine

Observatoire de Paris, Syrte

A Division 1 Working Group on ?Nomenclature for Fundamental astronomy? (NFA) was formed at the 25th IAU GA in 2003 in order to provide proposals for new nomenclature associated with the implementation of the IAU 2000 Resolutions. This WG is also intended to make related educational efforts for addressing the issue to the large community of scientists.Five NFA Newsletters were issued from October 2003 to July 2004 to discuss the proposed terminology. All the material has been posted on the NFA webpage (http://syrte.obspm.fr/iauWGnfa/ ). One important step has been the preparation of a NFA questionnaire including two parts: Questionnaire NFA/A on ?terminology choices? which was at first intended for the astronomical community, and Questionnaire NFA/B, for the Almanac Offices and related organizations. All the WG members and a few astronomers responded to QA and the main Almanac offices responded to QA and QB. The summary of the documents collecting the responses and comments to both Questionnaires and the responses to the questions of Newsletter 4 have led to draft Working Group recommendations and guidelines on terminology which are supported by explanatory documents. These draft recommendations and explanatory documents are under discussion by the WG and have to be submitted to a larger community before being submitted to the IAU together with a Resolution proposal to the IAU 2006 GA. The preliminary recommendations and future actions of the NFA WG will be discussed.

B. F. Chao, C. M. Cox

NASA Goddard Space Flight Center

Time variable gravity measurements have been made over the past few decades using satellite laser ranging, and more recently by the GRACE satellite mission with significantly improved resolution. The degree-2 harmonic components of the time-variable gravity contain important information about the Earth?s length-of-day and polar motion excitation functions, in a way independent to the traditional ?direct? Earth rotation measurements. In particular, the (degree=2, order=1) components give the mass term of the polar motion excitation; the (2,0) component, under the conservation of mass, gives the mass term of the length-of-day excitation. Combining these with yet another independent source of angular momentum estimation for the geophysical fluids (for example atmospheric angular momentum, in both mass and motion terms), can lead to new insights into the dynamics of the Earth rotation excitation processes. We will present some preliminary results.

Jean CHAPRONT & G?rard FRANCOU

Observatoire de Paris - SYRTE

Three numerical libration ephemeredes built by JPL (DE245, DE403 and DE405) and an analytical model improved with numerical complements fitted to recent LLR observations are compared. We consider 3 angular variables which represent the deviations with respect to Cassini's laws. After having referred the models to a unique reference frame, we study the differences between the models which depend on gravitational and tidal parameters of the Moon, and also on amplitudes and frequencies of the free librations. The differences vary widely depending of the above quantities. They correspond to few meters displacements on the lunar surface, reminding that LLR distances are precise to a centimeter level.Taking advantage of the lunar libration theory of Moons (1984) improved by Chapront et al. (1999) we represent the differences by Fourier series after a numerical substitution of the gravitational and free libration parameters. These results are confirmed by frequency analyses.Using DE245 as a basic reference ephemeris, we approximate the differences between the analytical and numerical model with Poisson series. The analytical solution - improved with numerical complements under the form of Poisson series - is valid over several centuries with an internal numerical precision less than 5 centimeters.

P. Charlot, A. L. Fey, C. S. Jacobs, C. Ma, O. J. Sovers, A. Baudry

Observatoire de Bordeaux - CNRS/UMR 5804

The current realization of the International Celestial Reference Frame (ICRF) comprises a total of 717 extragalactic radio sources distributed over the entire sky. We present results of an observing program carried out to densify the ICRF in the northern sky using the European VLBI network (EVN) and other geodetic antennas inSpitsbergen, Canada and USA. A total of 150 new sources, most of which selected from the VLBA Calibrator Survey, have been observedduring three such EVN+ experiments conducted in 2000, 2002 and 2003. The sources were selected on the basis of their sky location in order to fill the "empty regions" of the frame. A secondary criteria wasbased on VLBI compactness to limit source structure effects in theastrometric measurements. A comparison with the VLBA Calibrator Survey astrometric positions will be presented.

D. Coulot

IGN/LAREG and OCA/GEMINI

The main goal of this paper is to study the efficiency of space technique combination for computation of Earth's Orientation Parameters. We use four techniques : SLR, DORIS, GPS and VLBI and the parameters of interest are polar motion, universal time and nutation corrections with a 6-hour sampling. We use a homogeneous computational framework for all individual computations. We carry out a combination based directly on measurements of all techniques. The results are compared to time series obtained by international analysis centres and IERS' models.

Goran Damljanovic and Jan Vondrak

Astronomical Observatory, Belgrade

At the end of 20th century, the HIPPARCOS Catalogue was finished, and near 4.4 million astrometric optical observations (made at 33 observatories) of near 4.5 thousand HIPPARCOS stars used for the investigations of latitude/universal time variations were collected. Nowadays, these optical observations of different Earth rotation programmes are useful for the improvement of proper motions of HIPPARCOS data, because the HIPPARCOS ESAmission was less than 4 years long, short for the precise proper motions of double/multiple stars (mostly), and the long history optical observations (during the interval1899.7-1992.0) can improve them (at the first place, the long term part). It is in line with other similar jobs (TYCHO-2, GC+HIP, TYC2+HIP, ACT, ARIHIP, FK6(I), FK6(III)). The most recent one is the Earth Orientation Catalogue (EOC). Here, some results of improved proper motions in declination (of some HIPPARCOS stars) are presented; we used the optical observations of latitude variations made with Photographic Zenith Tubes (PZT).

Dasaev Rustam Rashidovich

Moscow Aviation Institute

The rotation of the Earth round an axes which is taking place through centre of masses practically is always considered irrespective of transition of centre of masses of the Earth round the Sun and concerning a barycentre of a system the Earth - moon. It is supposed, that between orbital and rotary movements there is no interaction. Modern level of an accuracy of definition parameters of the Earth rotation results in necessity to remove some simplifications in the accepted theory. In the work, on basis of space variant of a problem "a deformable planet - companion in a field of attracting centre", the dynamic aspects of the Earth rotation under an operation gravitational - having flown perturbations of the Moon and Sun are investigated. Approximate (average on fast variables) equation of movement is noted in canonical variables. On basis of the asymptotic analysis of the equations of motion the stablis performances oscillatory - rotary motions of a deformable Earth concerning centre of masses are certain. The specified periods (frequency) of axial rotation and chandler wobble are found. The comparison with datas of the spectral analysis is conducted.

O. de Viron, V. Dehant

Royal Observatory of Belgium

Using animations, we will show what is the Non RotatingOrigin. We will show how transformation between the Terrestrial Frame to the Celestial Frame were done previously , and how it can be done using the newsystem. We will also show the motion of the NRO.

Dehant V., de Viron O., Van Hoolst T.

Observatoire Royal de Belgique

Flow in the fluid outer core results in various geodetic phenomena observable from the Earth's surface or space. These phenomena include variations in the Earth's rotation (length-of-day (LOD) variations) and in the Earth's orientation (precession and nutation). Some of thesevariations can be observed by very precise space geodetic techniques and provide unique insight into the core, which can not be observed directly. In particular, the LOD observation gives constraints on the decadal core flow, and the very accurately observed nutations have proven to be very useful to determine values of several parameters of the Earth's interior presented in the paper. The conservation of angular momentum links the change in the Earth rotation with the variation of the core angular momentum, which is computed from an estimated core flow. Physically, the cause of angular momentum exchange between core and mantle is through coupling torques between core and mantle: topographic, electromagnetic, viscous, and gravitational torques. When estimating the core (and inner core) effect on nutation and polar motion, the Poincar? flow hypothesis is classically used. One may wonder, however, whether these flows give a good representation of the true core flow associated with polar motion and nutation. For the LOD variation, the core flows are deduced from variations in the magnetic field observed at the Earth's surface, assuming constant velocity on concentric cylinders about the Earth rotation axis. This results in torsional oscillations in the core which violate the basic hypotheses of Poincar? flow.

M. Efroimsky

US Naval Observatory

Both the Serret-Andoyer and the Delaunay sets of elements share a feature not visible with a naked eye: in certain cases, the standard equations render these elements non-osculating.Orbital elements, calculated via the standard planetary equations, come out non-osculating when perturbations depend on velocities. This complication often arises but seldom gets noticed. To keep elements osculating under such perturbations, extra terms must enter the equations, terms that will NOT be parts of the disturbing function (Efroimsky and Goldreich 2003, 2004). In the case of parametrisation through the Kepler elements, this willmerely complicate the equations. In the case of Delaunayparametrisation, these extra terms will not only complicate the Delaunay equations, but will also destroy their canonicity. Under velocity-dependent disturbances, the osculation and canonicity conditions are incompatible.Similarly, the Serret-Andoyer elements come out non-osculating when the perturbation depends upon the angular velocity of the top. Since a switch to a non-inertial frame is an angular-velocity-dependent perturbation, then amendment of the dynamical equations by only adding extra terms to the Hamiltonian makes these equations render non-osculating Serret-Andoyer elements. To make them osculating, extra terms must be added to the dynamical equations (and then these equations will no longer be symplectic).Calculations in terms of non-osculating variables aremathematically valid, but their physical interpretation isproblematic. Non-osculating orbital elements parametriseinstantaneous conics not tangent to the orbit. Their inclination, the non-osculating "i", may differ much from the real, physical, inclination of the orbit, given by the osculating "i". As an orbit is presented by points from osculating or non-osculating Keplerian conics, so a complex spin is composed of osculating or non-osculating Eulerian cones. Non-osculating Serret-Andoyer variables correctly describe aperturbed spin but lack simple physical meaning. For example, the customary expressions for the spin-axis' orientation, in terms of the Serret-Andoyer elements, will no longer be valid, if these elements are non-osculating. These expressions, though, will stay valid for osculating elements, but then the (correct) dynamical equations for such elements will no longer be canonical --circumstance ignored in the Kinoshita-Souchay (KS) theory which tacitly employs non-osculating Serret-Andoyer variables. This may be the key to the known discrepancies between the KS and SMART97, discrepancies pointed out by Bretagnon et al (1997).

Alberto Escapa(1) , Juan Getino(2) and J. M. Ferr?ndiz(1)

(1) Dpto. Matem?tica Aplicada. Universidad de Alicante. Spain (2)Dpto. Matem?tica Aplicada. Universidad de Valladolid. Spain

In the last years several works have dealt with the effect of the redistribution tidal potential on the Earth rotation, that is to say on the rotational effects of the additional potential due to the elastic deformations caused on the Earth by the Sun and Moon. However, analytical or numerical results derived by some of these approaches seem to provide significant discrepancies. In this research we compare some of these approaches when considering the motion of the (rotational) angular momentum axis of a perfect elastic Earth model. To this end, we revise the Hamiltonian formulation of this problem ([1]), contrasting this model with others specially well suited for the purposes of comparison ([2], [3]). Finally, we determine the source of the discrepancies and point out possible solutions to avoid them.[1] Escapa, A., Getino, J. and Ferr?ndiz, J.M., Influence of the redistribution tidal potential on the rotation of the non-rigid Earth, 2004 (to be submitted). [2] Krasinsky G.A., Rotation of the deformable Earth with the viscous fluid core. Communications of the IAA RAS, 2003, 157, 1.[3] Souchay J.and Folgueira M., The effect of zonal tides on the dynamical ellipticity of the Earth and its influence on the nutation. Earth, Moon, and Planets, 1998, 81, 201.

Alan Fey

U.S. Naval Observatory

It is well known that the ICRF has a less than desirable density ofsources on the sky, particularly in the southern hemisphere. Toaddress concerns about the non-uniform distribution of ICRF sourcesand to monitor sources for structural variations, various observingprograms have been initiated. The goals of these dedicated observingprograms include: 1) obtaining more accurate positions, 2) obtainingsource position stability information from time series at useful timeresolution, 3) densification of defining sources and 4) sourcestructure monitoring. The USNO currently has a joint program with theAustralia Telescope National Facility (ATNF) for astrometry andimaging of southern hemisphere ICRF sources. The goals of this jointUSNO/ATNF program are to image all southern hemisphere ICRF sources atleast twice for structure monitoring and to search for new astrometricsources for densification of the ICRF in the southern hemisphere. Inaddition, the IVS schedules regular CRF observations for the specificpurpose of maintenance of the ICRF. In recent years, these CRFsessions have concentrated primarily on observations of sources in thesouthern hemisphere. Recent results from these ongoing observingprograms will be summarized.

M. Folgueira, N. Capitaine and J. Souchay

Complutense University of Madrid (Spain)

For many applications in the fields of Celestial Mechanics and Astrometry, the coordinates (X,Y) of the Celestial Ephemeris Pole in the Celestial Reference System are extremely useful. They are for example the parameters to which VLBI is directly sensitive. It is therefore important to obtain the equations of the Earth?s rotation problem as function of these parameters. This would allow us to provide a precession-nutation model directly in the form recommended by the IAU 2000 Resolutions. With these considerations in mind, the main objective of this paper is to obtain closed exact relations for these Earth rotation parameters in a compact and self-consistent form. This is also the first in a series of aims carrying out the progress of the European DESCARTES Sub-project entitled: ?Advances in the integration of the equations of the Earth?s rotation in the framework of the new parameters adopted by the IAU 2000 Resolutions?. The first part of the paper contains a brief report of the mentioned project as a whole, featuring the background work that motivated the project, its aims and objectives and the general research design. Then, we describe the different sets of variables in the rotation of a body such as the Earth in order to discuss the suitable methodology to undertake. Finally, we present the process of construction of the new Earth rotation equations as function of the coordinates of the Celestial Ephemeris Pole and some preliminary results.

T. Fukushima

National Astronomical Observatory of Japan

In order to directly integrate the motion of ecliptic, we developed a new set of orbital variables (Fukushima 2004a, b). This is the final goal of our studies on the manifold correction methods, the seven works of which appeared in Astron. J. in 2003 and 2004. The new set consists of the orbital angular momentum vector, two on-the-orbit components of Laplace integral, and an orbital longitude reckoned from an origin on the moving orbital plane. To our surprise, the numerical integration of a quasi-Keplerian orbit using the new variable set has some remarkable features. First, the integration error of unperturbed orbit remains at the machine-epsilon level and never grows if sufficiently precise integration scheme is used. This is unchanged even if round-off are the main error source. For perturbed orbits, the errors grow in proportion to the square root of time for a sufficiently long time. These features are independent on the integrator used, the type of perturbations, and the policy of step size control.T. Fukushima, 2004a, Astron. J., 128, No.3, in printingT. Fukushima, 2004b, Astron. J., 128, No.3, in printing

D. Gambis, C. Bizouard, G. Francou, T. Carlucci and M. Sa?l

Observatoire de Paris

Besides computing combined Earth orientation parameters derived from the various space-geodetic techniques, one of the main tasks of the Earth Orientation Center of the IERS is to predict UT1-UTC variations for leap second announcements and DUT1 (Bulletins C and D). The Earth rotation rate variations are mostly due to geophysical phenomena that can be classified into two parts: seasonal terms due to atmosphere and oceans which are predictable with a fair accuracy and the long-term decadal variations so far attributed to core-mantle interactions. These long-term variations cannot be currently modeled and predicted with an sufficient accuracy, what statistically prevents to predict leap second occurrences beyond about 4 years. New methods based on the Singular Spectrum Analysis and Core Angular Momentum prediction are being investigated.

James L. Hilton

U.S. Naval Observatory

The IAU Working group on Precession and the Ecliptic was formed at the XXV General Assembly of the IAU, Sydney 2003, in response to requests for a dynamically consistent precession theory compatible with the IAU 2000A nutation theory. Since that time, the working group has made significant progress towards the adoption of just such a theory. This talk will look at the current state of the process and includes the author's thoughts on the definition of the ecliptic and a recommendation for an adjustment in the nomenclature of precession.

C. Hohenkerk

HM Nautical Almanac Office, Rutherford Appleton Laboratory

Following the IAU 2000 resolutions together with the implementation and availability of the various software routines, it became imperative that The Astronomical Almanac (AsA) included the IAU recommended techniques for applying precession-nutation. This involves introducing the Earth rotation angle (ERA), the adopted relationship between Universal Time (UT1) and the rotation of the Earth, together with the celestial intermediate origin (CIO), the corresponding origin for right ascension. The introduction of the CIO has been complicated by the fact that new nomenclature is required, which is in the process of being discussed and agreed by the IAU Working Group on Nomenclature for Fundamental Astronomy. The AsA continues to provides its users with all the equinox based data, tables and formulae that are provided each year. However, an attempt has been made in the 2006 edition to incorporate the new nomenclature and describe the process in a straight forward way with the intention of helping the diverse user community.

C.-L. Huang

Shanghai Astronomical Observatory

The relative motion, due to the Earth nutation, between the fluid outer core (FOC) and the mantle (and/or the solid inner core, SIC), causes a perturbation on the geomagnetic field near the core-mantle boundary (CMB) (and/or near ICB); this perturbed magnetic field (b) changes, in return, the motion of the earth and thus nutation, via the electro-magnetic torque (or Lorentz force) on the boundaries. In this work, we investigate the possible coupling between the nutation and b in numerical integration approach.In this numerical integration approach, the Lorentz force is added to the right side of the elastic-dynamic equations for infinitesimal elastic-gravitational motion for a rotating, slightly elliptical Earth; this Lorentz force is related to b and the initial magnetic field (B); b is related with nutation by induction equation and can be solved, while B in FOC can be obtained from a geodynamo model. We present here the strategy to deal with the Lorentz force in our numerical integration approach, including the solution of the perturbed field b, incorporating L into the scalar ordinary differential equation of nutation by generalized spherical harmonics, some dimensional analysis and approximation assumption, and iteration procedure. Finally, primary numerical result is presented and discussed.

D. Kiryan

Institute of Problems of Mechanical Engineering of RAS

It has been found that the residual (Chandler) motion of the Earth's rotation pole results from the forced translational motion of the Earth's rotation axis relative to the geographic axis. The Earth's rotation axis moves parallel to itself without changing the angle of inclination to the ecliptic plane. The translational motion of the Earth's axis of rotation is caused by the motion of the Earth's center of mass in the Earth's body in the range from 1 to 30 meters relative to the Earth's surface. The motion of the Earth's center of mass in space is due to the motion of the consistent inner core of the Earth in the liquid outer core under the action of the total (internal and external) gravitational field. Formulae for calculation of the trajectory of the Earth's centre of mass from astronomical observations are suggested. The comparison of our calculations and observational data on variations in the latitudes of places and acceleration of gravity has shown that they are in good agreement. Our model has been shown to adequately describe the physical process of motion of the Earth's centre of mass inside the Earth's body.

L. Koot, O. de Viron and V. Dehant

Royal Observatory of Belgium

Variations in the rotational speed as well as in the direction of the Earth rotation axis are due to the gravitational torque exerted by the Sun, the Moon and the other planets and to the interactions between the solid Earth and the geophysical fluids. The effects of the atmosphere on Earth rotation are classically computed using the angular momentum approach: the variations in the rotation of the Earth are estimated from the (opposite) variations in the atmospheric angular momentum (AAM). Several AAM time series are available, from different meteorological centers. However, the estimation of atmospheric effects on Earth rotation differs strongly when using one atmospheric model or the other. We build an objective criterion which justifies the use of one series in particular. We determine the quality of each series by making an estimation of their noise level, using a generalized formulation of the three-cornered hat method. As the quality of the series varies in time, we construct a combined AAM series, using time dependent weights chosen so that the noise level of the combined series is minimal. This quality criterion, while totally independent on Earth rotation observations, appears to be convincing when atmospheric and Earth rotation data are intercompared.

A. Korsun

Main Astronomical Observatory Ukrainian AS

E.Fedorov compared the calculated values of the nutation terms with Poincare theory of the rotation of the Earth with a liquid core. This was a pioneer work of such comparison results of latitude variations of the ILS stations with theory. The results of Fedorov's work were published in book "Nutation and forced motion of the Earth's pole" (Kiev,1958). This book was translated in English with a foreword by Sir H.Jeffreys (Pergamon press, 1963). The results of the comparison are discussed.

W. Kosek, M. Kalarus, T.J. Johnson, W.H. Wooden, D.D McCarthy, W. Popińsk

Space Research Centre, PAS, Warsaw, Poland

In this paper different stochastic prediction techniques including autocovariance, autoregressive, autoregressive moving-average, and neural networks were applied to predict UT1-UTC data. All known effects such as leap seconds, solid Earth zonal tides, and seasonal effects were first removed from the observed values of UT1-UTC. Different combinations of least-squares extrapolation and stochastic prediction methods were also applied. The results of the combined forecast methods were compared with the UT1-UTC prediction method currently used by the IERS Rapid Service/Prediction Center. It was found that the prediction accuracy depends on the starting prediction epochs and that the mean prediction errors of the combined forecast methods are of the same order as those of the method used by the IERS Rapid Service/Prediction Center.

O. Kudkay

Main Astronomical Observatory of NANU

Within the framework of nonlinear approach to the problem of Earth rotation the properties of full( not simplified) Liouville equations are explored. The system as it was found out is the singular one - left part terms( derivative's terms) contain small parameters and it's solution requires special methods application ,for example, regularization ( or others ) but not a regular perturbation technique as it's usually done after Munk and Macdonald . We discuss the dependence on variables choice and propose ways to overcome the difficulties. Difference between full and simplified system solutions above all consists of nonlinear effects which may significantly distort linear solution for example for wobble . One of them - oscillation of phase is able to bring to Chandler period variation and it's spectral peak broadening that back up old conception of "instantaneous period".

S. Kudryavtsev

Sternberg Astronomical Institute of Moscow State University

The original KSM03 harmonic development of the Earth tide-generating potential (TGP) [1] includes 26,753 terms of amplitudes down to the level of 10^{-8} m^2/s^2 and is made in a reference frame defined by the true geoequator of date with an origin at the point ? that being the projection of the mean equinox of date. The TGP series developed in that frame have TDB time argument and do not include a much less stable UT1 time argument which is necessary to calculate the TGP in the Terrestrial reference frame (TRF). Such an approach makes the series of KSM03 development valid over a long-term interval of time (1000AD-3000AD), and the relevant accuracy of the gravity tides calculation is estimated to be at the sub-nGal level. It exceeds the accuracy of any previously made harmonic development of the TGP in time domain by a factor of at least three. However, for practical applications it is valuable to represent the Earth TGP developments in the rotating Terrestrial reference frame. Therefore coefficients of the KSM03 series have been re-calculated in the TRF and then transformed into HW95 normalization and format (in total 28806 waves). The KSM03 harmonic development of the Earth TGP represented in such a form is available at http://lnfm1.sai.msu.ru/neb/ksm/tgp/ksm03.dat. It can be directly used by nutation theories and in precise calculations of various tidal effects observed in the TRF. The work is supported in part by grant 02-02-16887 from the Russian Foundation for Basic Research.Reference:1. Kudryavtsev S.M., Improved harmonic development of the Earth tide-generating potential, Journal of Geodesy, 2004, 77(12), 829-838

L.D. Akulenko, S.A. Kumakshev, YU.G. Markov

Institute for Problems in Mechanics

Perturbed rotatory/oscillatory motions of Earth under the action of the gravitational forces due to Sun and Moon are studied. In this study, Earth is regarded as a linear viscoelastic body. It has been established that the excitation of oscillations of the poles (more precisely, the vector of angular velocity of Earth in the Earth-fixed reference frame) has a tidal nature and can be accounted for by the rotatory/translatory motion of the Earth-Moon baricenter about Sun. It is shown that basic characteristics of these oscillations are rather stable and do not change during time intervals that substantially exceed the precession period of Earth's axis. Using methods of celestial mechanics, we construct a simple mathematical model governing these oscillations. This model involves two frequencies (natural (Chandler's) frequency and yearly frequency) and provides predictions that agree with IERS astrometric data. The parameters of this model were identified on the basis of the spectral analysis of the IERS data and least squares method. Using this model, we obtained statistically reliable interpolation data for time intervals from several months to several years. For the first time, a high-precision prediction of the motion of the poles for a term of 0.5 to 1 year and a fairly reliable 1 to 3 year prediction are presented. These predictions have been validated by observations during several recent years. The results obtained are of great importance for geodynamics and celestial mechanics, as well as for applications in astrometry, navigation, and geophysics.

Irina I. Kumova, Michael V. Stepashkin

Sobolev Astronomical Institute, Saint-Petersburg State University

The use of the SMART Earth's rotation theory supplemented with the relativistic indirect third--body (luni--solar) perturbations as exposed by Brumberg and Simon at the preceding Journees (Saint Petersburg, 2003) enables one to estimate the corresponding relativistic contributions in the GCRS -ITRS transformation. This Newtonian?type spatial rotation transformation includes five angles. Three of these angles represent Euler angles relating ITRS and KGRSC, kinematically non--rotating geocentric ecliptical system differing from GCRS by two elementary constant rotations. The differences of these Euler angles for Newtonian and relativistic SMART solutions result to relativistic contributions into GCRS-ITRS transformation. The numerical estimation of these values have been performed.

S. Lambert

U.S. Naval Observatory

We investigate the effects of the second-order terms usually neglected in the linearized dynamical equations of the non-rigid Earth's rotation. The second order torque on the Earth is function of zonal, tesseral, sectorial lunisolar potentials as well as increments of inertia. These increments of inertia are expressed as functions of the external potential (direct gravitational effects) and the wobbles (centrifugal effects), as a generalization of Sasao et al. (1980)'s formulae, using McCullagh's theorem. The effects of these terms on the precession-nutation of a stratified elastic oceanless Earth with fluid outer core are computed, yielding non-negligible contributions of zonal and sectorial tides interacting with tesseral potential (resp. 208 and 62 microarcseconds on the 18.6-y nutation in longitude) and a total effect of 7 mas/cy on the precession in longitude.Effects of anelasticity and ocean tides are being processed but they are not expected to contribute for more than a few microarcseconds.This work is an extension of Lambert & Capitaine (2004) [A&A, in press] concerning Earth's rotation rate variations and precession-nutation, itself clarifying the discrepancies between Souchay & Folgueira (1999) [EM&P, 81, 201], Bretagnon et al. (2001) [CMDA, 80, 177] and Mathews et al. (2002) [JGR, 107, B4].

C. Le Poncin-Lafitte, P. Tessandier

SYRTE, Observatoire de Paris

In highly accurate astrometric missions like GAIA and SIM, it will be indispensable to take into account the influence of the multipole structure of giant planets like Jupiter and Saturn on the propagation of light. We present an algorithmic procedure to determine this influence within the Nordtvedt-Will parametrized post-Newtonian formalism.

J.A.Lopez,M.J.Martinez,F.J.Marco

Universidad Jaume I de Castellon Spain

A tradicional method to study the orientation errors of the star catalogues is the analysis of the observation minus calculus residuals for a set of selected minor planets. Usually there are two problems: first, the distribution of the minor planet positions is not homogeneous in a band around the equator or the ecliptic, and second, the means in residuals are not null. Tradicional methods based on least squares could not work fine because of the hipotesis of Gauss-Markov theorem are not acomplished. In this work we present an alternative numerical method that is possibily more suitable in this case.

Chopo Ma

Goddard Space Flight Center

The VLBI data and analysis leading to the ICRF were completed in 1995. Since then there have been considerable refinements in both areas. In particular, advances in modeling the troposphere and station motions reduce systematic errors and permit integrated analysis of the celestial and terrestrial reference frames. Changes in instrumentation, networks, and scheduling, especially after 1990, improve the robustness and precision of the data. A regular monitoring program has begun to increase the data set for identified stable and potentially stable sources. Several steps need to be taken in the next few years to generate the next radio realization of the ICRS. These include: a) enhancement of the data set for possible defining sources, b) comparison of source catalogs from VLBI analysis centers using a variety of approaches and software to identify systematic errors, c) time series analysis of past and as-available data to identify the set of defining sources for the next realization, d) discussion and decision on the final analysis configuration, particularly for the data to be included, troposphere modeling, treatment of unstable sources, and whether a combination of normal matrices of individual solutions is better than a single selected solution.

F. J. Marco, M. J. Mart?nez, J. A. L?pez

Depto. de Matem?ticas. Universidad Jaume I. Castell?n. Spain

It is well known that the elliptic motion of a body is determined by metrical elements, connected with the size and shape of the orbit, and the angular elements, connected with the orientation of the orbit. On the other hand, the change of the Reference System could vary the orientation of the orbit including the inclination which, being a metrical element, contributes to determine the orientation of the orbit too. So, a temporal variation of the inclimation may indicate a geometrical initial variation or a bad initial determination of any physical parameter of both together things. This is a question that we shall study in our paper, in a first approach.

M. J. Mart?nez, F. J. Marco, J. A. L?pez

Depto. Matem?tica Aplicada. Universidad Polit?cnica de Valencia. Spain

After the publication of the Hipparcos and its acceptation as the Fundamental Reference Frame, the question of the homogenization of catalogues reemerged, because the IAU recommended that the necessary studies should be arranged in order to obtain as thorough relationships as possible with the rest of catalogues. A first step to arrange the comparative study of two catalogues (in particular Hipparcos and FK5 which are the Reference Frames of the new and old Reference Systems, respectively) is the application of a global rotation of one catalogue into the other.We employed two different models, including bias (GLAD model) or not (GL model) to obtain the infinitesimal rotations between the Hipparcos and FK5 catalogues. They provide different epsilon_z values, which is an important problem to be solved. To this aim, we use two different verification methods based on nonparametrical adjustement employing kernel regression (KNP) and spherical harmonics of order "n" (SHn). These methods are independent of the previously employed (GL or GLAD) and they give us an indication of the true magnitude order of the parameter searched.

D. McCarthy

U. S. Naval Observatory

The International Telecommunications Union Radiocommunications section (ITU-R) has created Special Rapporteur Group 7A on the Future of the UTC Time Scale, and it presents its final report in September, 2004. This report suggests potential alternatives to the current relationship between the UTC time scale and the Earth?s rotation angle as described by UT1. It is expected that this may lead to formal proposals to re-define this relationship. Possible consequences for the astronomical community are reviewed.

D. McCarthy

U. S. Naval Observatory

The International Earth rotation and Reference system Service (IERS) provides observational determinations of the celestial pole offsets that describe quantitatively the difference between the observed direction of the Celestial Intermediate Pole in the celestial reference frame and the direction predicted by the conventional precession-nutation model. The free core nutation is the most significant component of that time series. This motion is due to the fact that the rotation axes of the core and mantle are not aligned, and it is seen in the observations as a periodic variation with a period of 432 days with time-variable amplitude and phase. The IERS is tasked with providing a numerical model for this motion. The current status of the free-core nutation models is reviewed and their accuracy is assessed.

F. Mignard

OCA/Cassiopee

The European space astrometry mission Gaia is scheduled for a launch in 2011 and aims to produce a complete sky survey down to V = 20 with an astrometric accuracy of 10 muas at V = 15. During its 5-year mission the satellite will also repeatedly measure the position of ~ 500,000 quasars in a consistent way, leading to a direct realisation of the primary inertial frame in the visible within the ICRS concepts. At V =20 the sky density of the QSOs is about 1000 times smaller than that of the stars at mid galactic latitude, therefore the first problem to devise an automatic recognition scheme of the non stellar sources with a sensitivity of the order of one part in 10,000. I will report on our current approach, primarily photometric, and on the limitations of the realisation of the frame with the best selected sources due to random noise and to lensing by intervening galaxies.

M. Stavinschi, D. Gambis, G. MariŞ, V. Mioc, A. Oncica

Astronomical Institute of the Romanian Academy

We point out some possible correlations between the periodic variations of the solar activity and the Earth?s rotation, characterized by LOD (length of the day).The 26 months (0.46 cycles/year) and 10.5 years (0.95 cycles/year) cycles of solar variability are present in the LOD data spectrum.

M. Stavinschi, V. Mioc

Astronomical Institute of the Romanian Academy

Henri Poincar? was not only a honorary member of the Romanian Academy, but also an important collaborator of many Romanian mathematicians and astronomers. It is sufficient to mention Spiru Haret, the first doctor in mathematics at Sorbonne, or Nicolae Coculescu, the first director of the Astronomical Observatory of Bucharest. The 150th anniversary of the birth of the illustrious French personality offered us a good opportunity to study the relations he and two other Poincar?, Raymond and Lucien, had with Romania. For our study we used a series of documents, including the manuscript of a letter sent by Nicolae Coculescu to Poincar?, or the report about Henri Poincar?s stage in Romania, at Reşiţa, discovered in the Library of the Faculty of Mines in Paris.

J. Mueller

Institute of Geodesy (IfE), University of Hannover

To organize dedicated research in ?Earth rotation and global dynamic processes? a status report ? in German - has been prepared (Schuh et al., 2003), in which the status quo of Earth rotation research is presented and the essential shortcomings and requirements in recent research is pointed out. To achieve a joint treatment of this topic, a big project has been defined and proposed to the German Research Foundation (DFG) to get funding for about 10 sub-projects (with 13 co-workers). This so-called DFG research group comprises scientists from observation techniques, data processing/analysis and particularly modelling, the central aspect of the planned project. Here, it was important to cover all components which are relevant for the description of the Earth system with respect to Earth rotation and for a better understanding of the under-lying, global dynamic processes. Therefore, the research group consists of scientists and institutions from geodesy, geophysics, meteorology and oceanography, which have already contributed to dedicated Earth rotation projects. This presentation gives an overview about the planned research activities and the overall schedule.

Jolanta NASTULA and Daniel GAMBIS

Space Research Centre of the PAS

It is so far widely accepted that atmospheric and oceanic variabilities play an major role in the excitation of polar motion at period longer than 10 days. However for shorter periods the effect is not clear. We have reanalysed the role of Atmospheric Angular Momentum (AAM) and Oceanic Angular Momentum (OAM) variabilities on the excitation of high frequency polar motion variations taking advantage of a recent Oceanic Angular Momentum (OAM) series derived by Ponte and Ali. We show that they are significant at periods between 2 and 10 days. These results can bring confidence for discriminating between the different polar motion solutions obtained by the various analysis centers participating to the IERS Combination Pilot Project by comparing them to both Atmospheric and Oceanic Angular Momentum

J. Nastula, B. Kolaczek

Space Research Centre PAS, Warsaw, Poland

Detailed studies of the pressure terms of the regional atmospheric excitation functions of polar motion with high resolution containing 3312 grids in all glob were undertaken. Covariances, correlations, variances between regional pressure terms of the atmospheric excitation function and geodetic excitation function with such high resolution in the Eurasian region are computed and studied.

R. Popescu, A. Nedelcu

Astronomical Institute of the Romanian Academy

We show up the capability of the old Prin-Merz astrograph, completely renewed, to perform narrow-field astrometry. A highly accurate metrological system has been conceived in order to monitor, focus, and track the reference stars. Besides, a high quantum efficiency CCD camera based on a back illuminated chip, allows to this instrument to "observe" celestial objects up to 18 magnitudes, in less than 10 minutes of exposure. Due to the small FOV of the instrument we use the most dense star catalogue available - USNO B1.0 wich can provide us reference stars enough to compute an accurate plate solution. The rms of residuals is around 0.20-0.30" and the main source of scattering is in the USNO B1.0 catalog catalogue rather than in method used for image reduction. As an example we provide the astrometric positions inferred for 3908 Nyx (1980 PA) a Near Earth Asteroid which will have a close approach in 14 November 2004. All the data have been submited to the MPC.

V.V. Pashkevich, G.I. Eroshkin

Central (Pulkovo) Astronomical Observatory of RAS, St. Petersburg, Russia

The discrepancies of the comparison of the numerical solutions of therigid Earth rotation problem with the semi-analytical solutionsSMART97 are processed by means of the spectral analysis methods forthe kinematical and dynamical cases over the time interval of 2000years. In the result of the removal of the secular trends from thediscrepancies by the least squares method new temporal polynomials ofthe 6-th degree for the precessional parameters and GMST arereceived. The power spectrum of the periodical discrepancies isconstructed by using the set of the nutational harmonics of SMART97.Starting from the maximum term of the spectrum, each term of newnutational series is determined and removed from the discrepancies.The new nutational series consist of more than 9000 periodical terms.The comparisons of the high-precision numerical integrations of theproblem (with a quadruple precision) with new rigid Earth rotationseries demonstrate their good agreement. The discrepancies of thecomparison do not surpass 10 microarcseconds over 2000 years in Eulerangels. In the result of this investigation new semi-analyticalseries of the rigid Earth rotation, dynamically adequate to theDE404/LE404 ephemeris, are constructed over the time interval of 2000years.

Perepelkin Vadim Vladimirovich

Moscow Aviation Institute

The accurocies experimental observational data about trajectories of Earth?s pole motion testify about complicated dinamical process which are proceeding in Earth-Moon-Sun system. The construction of mathematical model which can describe real trajectories of rotation?s axis in some comfortable binded to Earth coordinate system is a very important problem in astronomy and geophysics.The theories which had already existed take into consideration many geophysical phenomena but doesn?t reflect essence of process of Earth rotation.In this work is used mechanic model of visco-elastic hard body which bases on the strict theorems of mechanics and methods of perturbations.It is interest and useful from science point of view more common problem which bases on the three-dimansional variant system of deformable Earth-Moon in a fild of attracting centre Sun. Moon and Sun are material points.On bases of the asymptotical methods nonlinear mechanical and mathematical modeling of equations of translational-rotational motion in Delone-Anduaje variables the qualitative analysis and quantitative estimate of complicated dinamical process of Earth?s rotation.

G. Petit and D.D. McCarthy

BIPM

The consistency of the reference frames provided by the IERS and its different centers relies on the set of conventional models and procedures that are used to realize them. These conventional models and procedures are mostly the product of the IERS Conventions Center, provided jointly by the Bureau International des Poids et Mesures (BIPM) and the U.S. Naval Observatory (USNO).The IERS Conventions (2003) were finalized in October 2003 and made available in November 2003. At the same time, work has been initiated in order to prepare the future updates of the IERS Conventions. Some technical issues are already identified as possible changes and are discussed in this report.New tools have been developed to help in the process of updating the IERS Conventions. A new web site and a discussion forum have been installed at the BIPM and are described.

S. Pireaux (1), JP. Barriot (2), P. Rosenblatt (2)

(1) UMR5562, Observatoire Midi-Pyr?n?es, (2) Observatoire Royal de Belgique

Today, the motion of spacecrafts is still described according to the classical Newtonian equations plus the so-called "relativistic corrections", computed with the required precision using the Post-(Post-?) Newtonian formalism. The current approach, with the increase of tracking precision (Ka-Band Doppler, interplanetary lasers) and clock stabilities (atomic fountains) is reaching its limits in terms of complexity, and can be furthermore error prone. In the more appropriate framework of General Relativity, we study a method to numerically integrate the native relativistic equations of motion for a weak gravitational field, taking into account not only gravitational forces, but also non-gravitational ones (atmospheric drag, solar radiation pressure, albedo pressure, thermal emission?).When considering gravitational forces alone, the unperturbed satellite motion follows the geodesics of the local space-time. For the appropriate metric at the required order, the latter equations contain all the gravitational effects at the corresponding order. Indeed, computing the geodesic equations for the Geocentric Coordinate Reference System metric (IAU conventions 2000) will take into account gravitational multipole moment contributions from the central planetary gravitational potential,perturbations due to solar system bodies, the Schwarzschild, geodesic and Lense-Thirring precessions. When non-gravitational forces are present, the relativistic equation of motion generalizes to include non-gravitational forces encoded in a quadrivector.Non-gravitational forces can be treated as perturbations, in the sense that they do not modify the local structure of space-time (the metric).We show here how to recover the classical equation for accelerometers from this relativistic formalism, hence how to measure the force quadrivector.

O. Bădescu, P. Popescu, R. Popescu

Astronomical Institute of the Romanian Academy

In this paper an algorithm for the simultaneous and at the same time rigorous determination of the astronomical coordinates is described: the latitude, longitude and astronomical azimuth, by means of a universal device (total electronical station). We have taken as a basis the azimuthal and zenithal angular observations for a large number of stars, uniformly distributed on the celestial sphere, without using observation ephemeredes. Through the introduction of an adequate matrix of weights,the unequal weights of all direct measurements are taken into account: the angular measurements and times at the chronometer. By applying the theory of conditional measurements with unknowns, we obtain one rigorous algorithm for the determination with maximum efficiency of all three fundamental elements of astronomical geodesy.

N. Rambaux, T.Van Hoolst, V. Dehant

Observatoire Royal de Belgique

We present a study of the dynamical behavior of a liquid core inside the Earth related to the mantle by inertial coupling. In order to integrate the terrestrial core-mantle interaction in a realistic model of the Earth's rotation, we have used our SONYR model of the solar System including the Earth's spin-orbit motion; SONYR is the acronym of Spin-Orbit N-bodY Relativistic model. By integration of the SONYR model, we obtain the dynamical behavior of the rotational motion of the Earth considered as a homogeneous body and as a model with two layers. The comparison of the dynamical evolution of these two models of internal structure permits to clarify the impact of the core's motion on the librations. We estimate the proper frequencies, the Free Core Nutation and the Chandler Wobble, of the two-layer Earth model. Moreover, we compute the dynamical motion of the core itself, and find that it has a larger amplitude than the dynamical motion of the mantle. Besides, we present results obtained for various initial conditions and for various oblatenesses.

Y. Rogister, M.G. Rochester

Ecole et Observatoire des Sciences de la Terre Strasbourg

The normal mode theory of a rotating Earth model isbased on the superposition of two perturbations. The first one is the perturbation of a spherically-averaged model of reference by rotation; it provides the rotating Earth model. The second one is a perturbation of the rotating model; it is a normal mode. In both cases, we consider Lagrangian perturbations. This implies that we define first a new coordinate system in the spherical configuration of reference. These coordinates, which are non-orthogonal, are such that the parameters of the spherical model depend on one of the coordinates only.The relation between the physical spherical coordinates in the rotating configuration and the new coordinates involves the radial discrepancy $h$ between the spherical model of reference and the rotating model. We assume that, prior to being perturbed, the rotating model is in hydrostatic equilibrium. We determine the shape of the rotating configuration to the second order in $h$, using the theory of hydrostatic equilibrium figures. Next, we write the equations of motion of the rotating model in the new coordinate system. We suppose that the stress-strain relation is linearly elastic and isotropic. By inserting the analytical solution for the tilt-over mode in the equations of motion, we show that the terms containing the initial equilibrium gravity must be computed to the second order in $h$. Finally, we separate the variables in the equations of motion by expanding the unknown functions on the basis of surface spherical harmonics. We obtain an infinite set of coupled first-order ordinary differential equations that, if truncated, is suitable for numerical integration.

C. Ron, N. Capitaine, J. Vondrak

Astronomical Institute, Prague; SYRTE, Observatoire de Paris

The new star catalogue EOC-2 has been used for the new solution of Earth Orientation Parameters (EOP) from optical astrometry in 1899.7-1992.0. The same procedures as in our preceding solutions were followed with two exceptions: 1. IAU 2000 nutation model and P03 precession model (Capitaine et al., 2003, A&A 412) were used which led to much smaller values of celestial pole offsets (CPO), 2. CPO in longitude and obliquity were represented by a constant, linear and square terms instead of the 5-day individual values asbefore. The obtained values of the linear and especially square terms of the CPO are compared and discussed in view of check of the P03 precession model over one century of astrometric observations.

David Salstein, Ben Chao, Rui Ponte, Jianli Chen, Yonghong Zhou

Atmospheric and Environmental Research

Products of atmospheric analyses and/or models are needed to calculate EOP excitations including length of day, polar motion, and nutation, the last dependent on the diurnal variability of the equatorial angular momentum. The Special Bureau for the Atmosphere (SBA) of the Global Geophysical Fluids Center of the IERS has been calculating, accessing, archiving, and distributing these excitation terms. Weather centers have supplied the bureau with operational and reanalysis series. The other geophysical fluid, the ocean, has diurnal terms as well, relevant to nutation, which may be estimated using models, and their quality and usefulness needs assessment. The subdiurnal series for the atmospheric excitation function for polar motion is the heart of the tasks. Atmospheric weather analysis systems typically produce 6-hourly values, the frequency of many observations. Some systems, like that at NASA GSFC, have produced some meteorological parameters every 3 hours; higher temporal resolution may yet be possible. We will also assess 3-D versus 2-D calculations of AAM and gravity Stokes coefficients, and redesign convenient and advanced methods of providing the community information. We thank the winners of the Descartes Prize for nutation studies with having awarded our team the support for a postdoctoral fellow for this purpose.

N. Shuygina

Institute of Applied Astronomy of RAS

Time series of Earth orientation parameters (EOP) are usually obtained independently from the processing of high accuracy modern observations such as VLBI, SLR, LLR, and GPS. This paper presents an attempt of determination of EOP from the joint analysis of LLR, SLR and VLBI measurements at the observational level. We used laser ranges to geodetic satellites LAGEOS, LAGEOS 2, and Etalon 1&2 taken from the Crustal Dynamics Data Informational System (CDDIS) and European Data Center (EDC). We also used VLBI observations of distant quasars obtained during the NEOS-A campaign. Lunar ranging data of 1970-2003 were added to the SLR and VLBI measurements. All these observations were processed by the program package ERA (Ephemeris Research in Astronomy), using the same astronomical constants and models for different kinds of measurements. Kalman filtering procedure was used to solve the system of conditional equations to determine corrections to local variables, as well as to common Earth rotation parameters. Combining LLR, SLR and VLBI measurements makes it possible to get standard deviations of UT1-UTC parameter smaller to compare with that obtained by means of each technique separately.

N. Sidorenkov

Hydrometcentre of the Russian Federation

The Decade' fluctuations of the Earth rotation velocity and the secular polar motion (DFER&PM) are usually explained by the interactions of the Earth?s core and mantle. This hypothesis well explains a close correlation DFER&PM with variations in the rate of the westward drift of the geomagnetic eccentric dipole and corresponds quite reasonably to the possible redistribution of the angular momentum between the fluid core and the mantle of the Earth. However, it can not explain the close correlations DFER&PM and the observable variations in the masses of the Antarctic and Greenland ice sheets, as well as with the decade oscillations of the types of synoptic processes (the epochs of the atmospheric circulation), with the global anomalies of the atmospheric pressure and temperature, regional anomalies of the cloudiness, precipitation, and other climatic characteristics. The new hypothesis is proposed that DFER&PM are the fluctuations of the velocity of the lithosphere drift along the asthenosphere. These fluctuations are due to the lithosphere moments of inertia variations owing to the redistribution of the water masses between the World Ocean and the Antarctic and Greenland' ice sheets. On the one hand, the atmospheric and oceanic circulations are responsible for the redistribution of water on the Earth?s surface, and on other hand, these circulations determine the global climatic conditions. The initial cause of the decade oscillations of the atmospheric and oceanic circulations are, probably, the gravitational interaction between the non-spherical and eccentrical envelopes of the Earth and the Moon, the Sun, and planets (J.V.Barkin, 2002). The astrometrical consequences following from this hypothesis are discussed.

Michael Soffel and Sergei Klioner

Lohrmann Observatory, Technical University, Dresden, Germany

First, some problems related with the ICRS, BCRS and the GCRS are mentioned. Recent work concerning the extension of the BCRS to include cosmic effects such as the global expansion of the universe is presented and special applications are treated.Then the problem of (stellar) places in the frameowrk of Relativity is discussed in some detail. A new way how to introduce relativistic spatial reference axes for some Earthbound observer is presented. Recent work to describe Earth's rotation in the framework of Relativity is described. Improvements have been achieved for the relativistic description of an elastic Earth by means of a displacement field.Unfortunately no progress has been achieved to generalize present formalisms for a rigid Earth to be conisistent with Relativity.

Michael Soffel and Sergei Klioner

Lohrmann Observatory, Technical University, Dresden, Germany

The general problem of astronomical reference-systems and frames in the framework of Relativity is discussed. This part focuses on the ICRS, BCRS and GCRS and their relationships. Various arguments that might play a role in the problem of nomenclature are given.

J. Sokolova

Astronomical Institute of St.-Petersburg State University

We studied the cumulative effect of the early VLBI observations (before 1990year) on the source catalogue stability. Five CRF solutions on different timeintervals have been obtained using the Occam6.0 software. All sources weretreated as global parameters. Calculation of the estimated coordinatedifferences between the individual solutions provides criteria for detectionof the highly unstable sources. Several sources with high visible motions aredetected.

M. Soma, K. Tanikawa

National Astronomical Observatory of Japan

We have shown that the parameter TT-UT for the Earth'srotation angle had periodic behavior whose period wasseveral hundred years in addition to the quadratic termof the time. We show here that using the ancient solareclipses which were observed as total or very deep atplural sites we can gain the accuracy of the TT-UTvalues. One of such examples of the solar eclipses isthe BC 188 July 17 eclipse, which was observed and recordedboth in Changan in China and in Rome in Italy, which leadsto the value of TT-UT between 12581 sec and 12741 sec in BC 188.

Jean Souchay , Ralph Gaume

Observatoire de Paris, Syrte; US Naval Observatory

From January 2001, Paris Observatory and the US Naval Observatory (USNO) propose to act jointly as the International Celestial Reference System Product Center of the IERS. We present herafter the present various activities of this Product Center, insisting on particular future prospects (GAIA, pulsar timing etc...)

B. Bucciarelli, M. Lattanzi, G. Massone, A. Poma, Z. Tang, S. Uras

INAF - Istituto di Radioastronomia - Cagliari (Italy)

The method of photographic observations as applied to the optical link of the VLBI-defined celestial reference frame was commmonly carried ou in two steps, by combining the capabilities of medium and long-focus telescopes. A by-product of this technique is the realization of astrometric fields around each QSO target, with an accuracy typically in the range of 50 to 100 milliarcseconds, and therefore suitable for a varieties of astrometric studies. We present here some results derived from plates collected during a photographic campaign on 89 QSOs, carried out by Torino Observatory and digitized at Cagliari Observatory.

Varga P., Gambis D., Bizouard C., Bus Z.

Geodetic and Geophysical Research Institute, Observatoire de Paris

Authors try to answer three questions:1)Can influence a single seismic event in perceptible degree the length of day?2)Is there any correlation between the seismicity and variations in LOD?3)The seismicity influencing the axial rotation or inversely the changes in LOD influencing temporal changes of seismicity of the Earth?With the use of theoretical models of an elastic radially inhomogeneous Earth with liquid core it is shown that even the stress accumulation and drop in case of giant earthquakes(M~9)are not able to produce variations in LOD bigger than 10 microsecond. A comparison of temporal and geographical distribution of earthquakes M=7 and greater with the LOD variation during XXth century confirms that the seismic activity of the Earth is influenced by LOD variations.

J. Vondr?k, C. Ron

Astronomical Institute, Prague

We collected and analyzed the astrometric observations of latitude / universal time variations made worldwide at 33 observatories in the 20th century. These observations, referred to Hipparcos Catalogue, were then used to determine Earth Orientation Parameters (EOP) at 5-day intervals, covering the interval 1899.7-1992.0. The analysis of the residuals revealed soon that many Hipparcos proper motions (especially of double stars) required significant corrections. Later on, new astrometric catalogues (such as ARIHIP or TYCHO-2) appeared as combination of Hipparcos / Tycho positions with ground-based catalogues. These catalogues yield more accurate proper motions (in a long-term sense) than original Hipparcos Catalogue. Our attempt goes however even further - we use about 4.5 million observations of latitude / universal time variations that we collected in the past, and combine them with these catalogues to obtain Earth Orientation Catalogue (EOC). The goal is to provide an accurate and stable reference frame (given on International Celestial Reference System), suitable for long-term Earth rotation studies. The second version of the catalogue, EOC-2, is presented. It contains 4418 different objects (stars, components of double stars, photocenters), observed in different Earth rotation programmes during the 20th century. The improvement of the accuracy of proper motions (especially in declination) over Hipparcos is remarkable - median sigmas attain 0.70 and 0.35 mas/year in right ascension and declination, respectively (compare with median Hipparcos values 0.87 and 0.85 mas/year).

P. Wallace

CLRC / Rutherford Appleton Laboratory

Pointing a telescope (or radio antenna) at celestial sources is, by the usual fundamental-astronomy standards, a rather low-accuracy application. Predictions of only 100 mas accuracy would in most respects be adequate, and this is well within the capabilities of even the pre-2000 models and procedures. However, the positional-astronomy part of the pointing application involves a long chain of transformations and corrections that has to be understood by both the astrophysicists who will use the telescope and by the engineers who will develop the control systems. These users, as well as being non-specialists in positional astronomy, have, with few exceptions, encountered only the old equinox-based methods. In addition, considerations of real-time computing efficiency usually make it necessary to calculate different effects and coordinates at differentrates, rather than a straightforward end-to-end transformation for a given moment in time, introducing the need to label various "in-between" coordinates. All of these factors make telescope pointing a good test case for the post-IAU-2000 nomenclature. How easy is it to describe to a non-specialist how to point a telescope, and does the introduction of the new paradigm help or hinder this elementary task?

W. H. Wooden, T. J. Johnson, P. C. Kammeyer, M. S. Carter, A. E. Myers

U. S. Naval Observatory

According to the terms of reference of the International Earth Rotation and Reference Systems Service (IERS), the Rapid Service/Prediction Center (RS/PC) is responsible for producing Earth orientation parameters (EOP) on a rapid turnaround basis, primarily for real-time users and others needing the highest quality EOP information sooner than that available in the final series published by the IERS Earth Orientation Center. The IERS Bulletin A and its associated data files contain preliminary and predicted EOP information including Universal Time (UT1). This paper focuses on the RS/PC's current combination and prediction process for UT1, recent improvements to the process, accuracy of the current solutions, and planned improvements.

Yatskiv Ya.S., Bolotin S.L., Kur'yanova A.N.

Main Astronomical Observatory of National Academy of Sciences of Ukraine, Kiev, Ukraine

Short overview of the activity of the Main Astronomical observatory of National Academy of Science of Ukraine (MAO) for maintenance and extention of the International Celestial Reference Frame (ICRF) is presented. Special attention is paid on the time stabilities of positions of radio sources (RS) and on the selection of a subset of RS to be used for maintenance of the ICRF. It is shown that seven RS qualified by the IERS as defining sources are unstable.

Y. Yu, Z.-H. Tang, J.-L. Li, M. Zhao

Shanghai Astronomical Observatory, Chinese Academy of Sciences

Since the field of view of a CCD is usually too small to cover enough reference stars, the block adjustment (BA) of CCD overlapping images is proposed in order to extend the sky coverage of observations, mitigate the effect of the position biases of reference stars, and consequently improve the local reference frame (LRF) of the observation (Yu et al, 2004). We have developed the program package of BA (SHAOBAP) and its flowchart is given. Some extragalactic radio sources were observed by the 2.16m telescope at Xionglong station of the National Astronomical Observation of China (NAOC) in 2004 June. We present the results of the determination of their optical positions by BA.

B. Zhang, J.-L. Li, G.-L. Wang, M. Zhao

Shanghai Astronomical Observatory

In the astrometric and geodetic VLBI data analysis software CALC/SOLVE system, the high frequency variations of the Earth Rotation Parameters (ERP) are determined by a constrained continuous piecewise linear model, that is, the ERP rate within two epoch nodes is constrained to be smaller than a limitation setting, and the ERP is forced to be continuous at epoch nodes. Observation analysis shows that when the data points are not very dense the constraint and the continuation requirement are helpful to improve the stability of the solution, but degrade the independence of ERP solutions at epoch nodes. In addition, the rate constraint and the solution segment length should be properly determined by the analyst based on the real situation of observations. By using the UserPartial feature of CALC/SOLVE a direct solution module of the high frequency variations of ERP is realized without using any constraint on the rate nor the requirement of continuation at nodes. It is shown from observation reduction that the direct solution mode is feasible. In the solution of high frequency variations of ERP from VLBI observations with long period coverage, the model errors of precession and nutation (celestial pole offset) should be taken into consideration. A corresponding module is also realized and global solutions of the high frequency variations of ERP are successfully performed on the VLBI observations from 1979 to 2003. Comparison of the solutions shows that with the consideration of the pole offsets the precision of parameters could be improved obviously. In the solution of high frequency variations of ERP from VLBI observations, the direct solution mode with the consideration of the celestial pole offsets is accordingly recommended.

V.E. Zharov

Sternberg State Astronomical Institute

Different packages OCCAM and ARIADNA were used for calculations of corrections for modern nutation series from the VLBI data. It was shown that the Free Core Nutation parameters depend on both the reduction procedure and used nutation theory. Reasons of these distinctions and models of predictions of the the FCN parameters are discussed in report.

Z. Zhu, H. Zhang

Departmemt of Astronomy, Nanjing University, China PR

Based on Hipparcos proper motions of the O-B5 stars, a clear warping motion has been found (Miyamoto & Zhu, 1998). Analyzing Hipparcos proper motions and radial velocity data for classical Cepheids, a slight contraction of the Galaxy in the solar neighbourhood seems to be suggested (Zhu, 2000). In order to reexamine the local kinematics of the young population of stars, we have selected about 1500 O-B5 stars. Combining the transverse velocities and radial velocities, we have confirmed the warping motion that is about the axis pointing to the Galactic center, while no contraction has been detected for the present analyse.