Because of the nature of observations with the HIPPARCOS, the observations will be reduced to a set of positions, motions, and parallaxes with respect to a rigid reference frame (HIPPARCOS Instrumental System). This reference frame will have an unknown a priori rotation with respect to both an inertial reference frame and an extragalactic reference frame.

The HIPPARCOS Star Mappers were designed to determine the satellite attitude by observation of stars with known positions. ESA has now enhanced them so that the continuous photon counts from two photo multipliers with B and V response will be recorded. The records will be used to derive an astrometric and photometric catalogue, the TYCHO Catalogue, complete to about B=11 mag and thus containing about 500 000 stars. The positions, annual proper motions and parallaxes will have an accuracy of about 0.03 arcsec and the magnitudes one of 0.03 mag.

The instrument is described and some aspects of the data reduction are discussed, namely the evaluation of a photon record by means of numerical filters, and the use of a TYCHO Input Catalogue.

A general overlapping-plate reduction program, REDUCE, has been written for the reduction of astrometric data from the Edwin P. Hubble Space Telescope. Pains have been taken to make this program powerful and flexible, yet easy to use. This paper describes the main features of the program.

Basic Fine Guidance Sensor data have been simulated to correlate the Power Spectrum Densities (PSD) of the Space Telescope motion disturbances with the “seeing” of an astrometric target. The goal of this study is to describe whether a complete identification of the jitter of the line of sight during an astrometric observation is required to improve the precision of this observation. The present preliminary results indicate that the performance in Astrometry are close to the predictions.

A new index catalog of visual double stars, the Washington Double Star Catalog (WDS), 1984.0, is now available in tape form. All of the double star data has been updated, as well as the notes to the catalog. This report summarizes the contents of the WDS and describes its compilation.

Astrometric desiderata for nearby stars concern, in first line, the parallax measurements, avoidance and elimination of effects of bias in trigonometric parallax programs: Bias towards large proper motions, preference of parallaxes with positive accidental errors, the Malmquist bias. For some of the nearby stars we do not yet know accurate positions, for some other objects no reliable proper motions were measured. Finally, for calibrating color-luminosity relations the necessity to observe further precise trigonometric parallaxes is demonstrated and emphasized.

The results of observations of Southern Reference Stars (SRS) of all participants in the SRS program (1961–1973) have been received at the U.S. Naval Observatory. It is anticipated that compilation of the final SRS catalog of mean positions will be completed by the end of 1984.

A supplementary list to the International Reference Star (IRS) catalog is described. It has been selected with a view to improving areal density and distribution in spectral type.

A comparison of solutions for equator and equinox corrections and corrections to the assumed elements of the earth's orbit from daytime observations of the Sun, Mercury, and Venus and nighttime observations of Ceres, Pallas, Juno, and Vesta from Six-inch Transit Circle observations made during the W5-50 program (1963–1971) shows that a very significant part of the systematic daytime error has been removed. A problem remains for observations of the Sun, particularly in declination.

The planetary and lunar ephemerides have their own inherent reference frame which is one of the key frames to be considered in the unification of the many present day frames, both celestial and terrestrial. The use of this frame requires an understanding of its own accuracies, both internal (i.e., relative) and external(e.g., w.r.t. the FK4 system or w.r.t. the dynamical equinox). Such accuracies are discussed in this paper. Also noted are the expected improvements in the future which will be obtained from newer data types.

During the last decades, regular meridian observations of the Sun and major planets have been mainly carried out at Washington and Greenwich observatories. However, after 1960 position observations of Solar system bodies were initiated at many observatories throughout the world. The photographic and the equal altitude methods are widely used at this time, besides the meridian method. According to available information, during the time interval from 1960 to 1980,altogether 19 meridian instruments, 12 astrographs and 5 astrolabes took part in observations of the Sun and the major planets. More than 40.000 observations of single coordinates - right ascension and declinations have been obtained.

The Soviet astronomers B.P. Gerassimovich and N.I. Dneprovsky suggested in 1932 that a Catalogue of Faint Stars be compiled. The SRS catalogue is in fact a realization of this suggestion for the southern hemisphere. The final goal of the work is an international catalogue of faint stars IRS=AGK3R + SRS, containing about 40 000 stars of the 7–9th mag. evenly distributed over the celestial hemisphere at the rate of one star per square degree. This catalogue could supply reference coordinates for astrometric studies of the Universe.

An astrometric standard catalog has been derived for the region centered on the Praesepe open star cluster. This catalog includes positions and proper motions of 408 objects on the system of the FK4 reduced from 9 catalogs and 145 plates from 15 different telescopes and spanning 110 years. The accuracy of the positions ranges from 0.01 to 0.15 arcsec and for the proper motions from 0.0002 to 0.004 arcsec/yr, depending on the number and quality of the observations. The method of catalog construction is an application of the central overlap technique.

Capabilities of the Danjon astrolabe and its transformations (with full pupil, photoelectric device, for Sun) are examined regarding both fields of instrumental modifications and improvement of the reduction techniques. For bright objects (stars and radiostars, planets, galilean satellites, Sun) these instruments will insure a valuable contribution to results obtained by the other techniques.

A brief description is given of the program of radio star observations with the Danjon Astrolabe of Santiago. Results in alpha (Astr.-Cat.) for radio star FK4 309, obtained from observations made at its east transit solely, are given for yearly periods of observation from 1976 to 1982. The average mean error of Δα is 0s.006.

The Guide Star Selection System (GSSS) will provide relative positions of two guide stars and the target for each observation of the Space Telescope as well as photometry for the guide stars. Being developed at the Space Telescope Science Institute, the GSSS is a production system which is based on PDS measurements of Schmidt survey plates. The specified accuracy for the system is +/−0.33 arcsec for the separation of the guide stars and 0.4 mag in the bandpass of the Space Telescope's Fine Guidance Sensors. The GSSS will produce two catalogs which will be used in the operation of the system. The Guide Star Photometry catalog includes photoelectric measurements (+/−0.05 mag) in B and V for six stars over the guide star range, 9.0 to 14.5 visual magnitude, near the central part of each 6 by 6 deg survey plate. The Guide Star Catalog will include the list of all possible guide stars and brighter, positions (at least +/−1 arcsec) and magnitudes (at least +/−0.4 mag) for essentially the whole sky complete to visual magnitude 15.

The space age and modern technology have opened a new era for astrometry. A great amount of modern, precise astrometric data and approaches is urgently needed not only for astrophysics but also for Earth Science research. The Astrometric Community looks forward to establishing a precisely specified uniform celestial frame of reference for all purposes, which will link the bright stars, faint stars, and galaxies, down to the remote radio sources, and to establish a terrestrial frame of reference as well as to specify a precise transformation between these two frames. Effective international cooperation is the goal of all astrometrists. The Chinese astronomers are ready to join and play an active part in this cooperation.

The convention for numbering radio sources adopted by the IAU uses the 1950 coordinates of right ascension in hours and minutes, followed by the declination truncated to tenths of a degree. It was designed for a growing population of sources so that new sources may be added and given an IAU number, unlike, for example, the listing in the BD catalogue which is a closed assembly.

The acquisition, preparation and distribution of machine-readable astrometric data by the Astronomical Data Center (ADC) are described. Examples of certain general changes in data structure and format to improve compatability with other computers and software processing systems and to increase storage efficiency are discussed, as are the present data archive and request history of the ADC. Current development work in the areas of astrometric and positional catalogs is described.

The present status and practice in the fundamental astrometry are analysed, and relying upon the findings the author suggests the organization of an international action aimed achieving better co-operation in the star position observations and celestial reference system determinations, as well as performing the intercomparison of the different techniques and methods.

The optical and radio positional reference systems are reviewed. A preliminary comparison indicates that the two do not at present agree to better than 0″.2 or 0″.3.

At present it is evident that the stability of a celestial coordinates system with an accuracy of at least per century, with respect to an internal frame can be derived only from VLBI observations of compact extragalactic radio sources. At the same time it is expected that the need for improved stars' coordinates will be strongly felt at least up to the end of this century, because stars are important and more convenient observational objects then very weak extragalactic sources or artificial Earth satellites (AES). One therefore wonders if one can use the high precision and stability of the radio astrometric reference frame to stabilize and improve the reference frame given by star catalogues. The problem of the relationship between these systems has so far been investigated in the form of determining the parameters of their mutual orientation, and/or studying systematic errors of star catalogues (Gubanov, 1978; Gubanov and Kumkova, 1978, 1981). This problem has been attacked by direct photography of several optically identified radio sources or VLBI observations of few radio stars. The present paper shows the feasibility of determining the place of any star of sufficient magnitude with reference to the radio astrometric frame, as given by extragalactic source positions (Gubanov, 1983). This is done by introducing an AES, equipped with radio signal for VLBI observations and a corner reflector for laser ranging, which can be observed by radio methods as well as optically (Gubanov, 1976). This satellite should also be bright enough in the reflected sun's light to be observed in the star field with a precision photoelectric satellite camera.