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By J. Kovalevsky, M. Froeschlé (auth.), Ivan I. Mueller, Barbara Kołaczek (eds.)

In this overview speak, i need to document at the right movement research, which has been lately performed including M. Soma and M. Yoshizawa: there was a chronic call for in astronomy for exact stellar positions and correct motions, that are represented via an inertial reference method developed at the foundation of a suite of constant astronomical constants. within the reference approach the precessional consistent performs a main function. In a sequence of papers Fricke (1967a,b, 1977a,b) has deter­ mined the luni-solar precessional correction to Newcomb's price and the fictional movement of the equinox, which were followed within the "IAU (1976) approach of Astronomical Con­ stants". in keeping with the precessional correction and the equinoctial movement therefore demonstrated, the elemental reference procedure, the FK5 procedure (Fricke et al. 1988) for positions and correct motions, has been built. notwithstanding, for numerous years geodetic VLBI (McCarthy & Luzum 1991) and LLR (Williams et at. 1991) observations were suggesting an extra correction to the luni-solar precessional consistent of the IAU (1976) method. that's, those observations point out the precessional correction of 6. p ~ -0:'30/cent to the FK5 method. yet, the observational interval ofthe earth orientation is taken into account to be nonetheless inadequate to split unambiguously the precessional switch of the earth orientation from the nutation with the longest interval of 18. 6 years.

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Additional resources for Developments in Astrometry and Their Impact on Astrophysics and Geodynamics: Proceedings of the 156th Symposium of the International Astronomical Union Held in Shanghai, China, September 15–19, 1992

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999998. 999 994 but improvement is expected in the next few years. The performance of a hypothetical Hipparcos-2 will be compared with that of Hipparcos (here called Hipparcos-l), assuming the same aperture of 29 em, but using two beamcombiner telescopes in order to improve the rigidity of the great-circle measurements. Abbreviations: 'H-1' stands for the Hipparcos mission, 'H-2' for Hipparcos-2, 'mas' for milli-arcsec, 'Hz' for counts/s or electrons/s, and 'PH' refers to Perryman & Hassan (1989).

The plane of the ecliptic is determined to within 1 mas while the parameters corresponding to the orientation in this plane have the lowest precisions. 11'0 and Wz . 5 years simulation. z ; W: SYSTEM ROTATION 0"15 o o 47850 200 <.. jd) TIME 400 (day) Figure 1 : Smoothed o-c 4. ADJUNCTION OF GROUND-BASED OBSERVATIONS We suppose that the planets and the Earth have all circular orbits in the plane of the ecliptic and we restrict the unknowns to the corrections to the mean longitude of the Earth (~L'O) and of a planet (~Lo).

Kovalevsky (ed), 281. INERTIAL FRAME DETERMINATION FROM HIPPARCOS OBSERVATIONS OF MINOR PLANETS. D. HESTROFFER Bureau des longitudes 77 Avenue Denfert Rochereau 75014 Paris France ABSTRACT. Observations of 48 minor planets by Hipparcos should lead to a good determination of the inertial reference frame. Analysis of one year observations showed periodic effects in the o-c due to a rotation between the Hipparcos system and the inertial system. 5 years simulation and by studying the impact of added ground-based observations, it appears that the orbital elements of the Earth and the parameters of a rotation of the system can be obtained with an accuracy better than 5 mas.

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