In this paper, all the light-curves obtained during the PHEMU91 campaign of observations of the mutual phenomena of the Galilean satellites are presented. These observations give accurate astrometric positions of major interest for dynamical studies of the motion of the Galilean satellites. The aim of this work is to give observational data directly usable for theoretical studies. We made 374 observations of 111 mutual events from 56 sites. The corresponding data are given in this paper(1). The accuracy of each observation has been deduced from a comparison with the theoretical predictions. For each observation, information is given about the telescope, the receptor, the site and the observational conditions.

Lagrange and Laplace were two of the first members of Bureau des longitudes which, among other tasks, were responsible for the improvement of astronomical tables and the progress of celestial mechanics. Between 1795 and 1850, many improved tables were published under the auspices of Bureau des longitudes: tables of the Sun by Delambre (1806), of the Moon by Burg (1806), Burckhardt (1812) and Damoiseau (1828), of Jupiter, Saturn and Uranus by Bouvard (1808, 1821), of Mercury by Le Verrier (1844), of the satellites of Jupiter by Delambre (1817) and Damoiseau (1836). In his tables, Bouvard showed there was a problem for Uranus. This led to the calculations of the elements of an unknown planet by Le Verrier and Adams and the discovery of Neptune in 1846. Le Verrier's calculations were published in Connaissance des Temps for 1849. In the second half of the XIXth century, two prominent members of Bureau des longitudes, Le Verrier and Delaunay, made major contributions to celestial mechanics by building elaborate theories for the motions of the Sun, the planets and the Moon. Other theories, which improved the above, appeared elsewhere at the end of the century, especially those of Newcomb, Hill and Brown. During the first half of the XXth century, there was a decline of the studies in celestial mechanics which seemed to have reached its limits owing to the difficulties of the computations involved. Yet Sampson's theory of the motion of the satellites of Jupiter and Chazy's first attempts to introduce general relativity into classical celestial mechanics should be quoted. In 1961, thanks to A. Danjon, Bureau des longitudes was reorganized so that its computation service became a research laboratory where, since then, important work in the theories of the planets, the Moon and the satellites has been made.

The ESA satellite Hipparcos provides valuable photometric and astrometric results on minor planets and natural satellites. Observations of 48 asteroids, JII-Europa, S VI-Titan and S VIII-Iapetus were made from November 1989 to March 1993. A twenty seconds averaged normal place is constructed, providing thus positions accurate to a few hundredths of arcseconds and relative to a very precise and homogeneous reference frame.

After the processing of 30 months of the observations carried out by Hipparcos it is possible to provide a reliable idea of the astrometric results to be obtained on the 48 minor planets included in the observing programme. Hipparcos observations are one-dimensional measurements of the separation of objects along a precessing scanning circle, these scanning circles are averaged over approximately 0.3 day yielding a reference great circle. The main output will consist of about 100 astrometric abscissae on a reference great circle for each minor planet with an individual accuracy of about 0.02 arcsec. We discuss in this paper the reduction procedure and assess the systematic errors due to the shape and scattering properties of the asteroids. The use of the results to improve the orbital parameters of the minor planets as well as the link of the kinematical and dynamical frames is briefly touched upon in the last section.

Every three years the IAU/IAG/COSPAR Working Group on Cartographic Coordinates and Rotational Elements of the Planets and Stallites revises tables giving the directions of the north poles of rotation and the prime meridians of the planets, satellites, and asteroids. Also presented are revised tables giving their sizes and shapes.

The main goat of Hipparcos is to build a catalogue of stars but 48 minor planets are bright enough and sufficiently pointlike to be observed also. This paper describes some aspects of the minor planets astrometric data reduction procedure. Comparison to the calculated places is given as well as a first attempt to minor planets orbital elements correction. The data collected after a year and a half show that minor planets position can be given with an accuracy of about 0.01 arcsecond. This great precision is balanced by the fact that observations are insufficiently numerous and not uniformly distributed to yield valuable results on the part of the osculating elements.

In addition to its astrometric capabilities the Hipparcos main detector proves to be a good phototometer. The main features of the photometric reduction applied to minor planets are outlined. The apparent magnitude measured by Hipparcos is transformed into absolute magnitude after corrections for the distance to the sun, the earth and for the phase effect, are applied. We show that the remaining signal contains information on the rotational properties of the planets.

In this paper, all the usable light curves obtained during the PHEMU85 campaign of observations of the mutual phenomena of the Galilean satellites are presented. These observations will provide accurate astrometric positions of major interest for dynamical studies of the motion of the Galilean satellites. The aim of this work is to give observational data directly usable for theoretical studies. We made 166 observations of 64 mutual events from 28 sites. The corresponding data are given in the present paper and compared with the theoretical predictions. The accuracy of each observation has been determined. For each observation, information is given about the telescope, the receptor, the site and the observational conditions.

The observation of minor planets by Hipparcos offers the opportunity to obtain high precision positions for some minor planets. About fifty minor planets are on the programme. Their ephemerides had to be improved in order to reach a precision of 1 arsec and occultations by the Earth and the Moon had to be predicted.From the position of a minor planet on reference great circles at different times better values of the initial position and velocity will be deduced but the reduction of the observations of the minor planets have to take into account the displacement of the photocentre relative to the centre which is due to the shape, the phase effect and the scattering properties of the surface. For some very small planets considered as star like this diplacement will be small and the precise positions obtained will allow to position the dynamical reference system relative to the Hipparcos system. For the bigger minor planets the observations by Hipparcos may give informations on the shape and scattering properties of the surface.

It was the President’s sad duty to report the deaths of two former past Presidents of the Commission, W. Fricke who had also been a Vice-President of the IAU and a President of Commission 8, and D. H. Sadler who had been Superintendent of H.M. Nautical Almanac Office from 1936 to 1969 and was once General Secretary of the IAU.

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