In 1964 a conference was held at Flagstaff, Arizona, in honour of Ejnar Hertzsprung. At this conference Martin Schwarzschild presented the inaugural address. The title was ‘New Impetus to Astrometry’. I was so much impressed by everything what he, as an astrophysicist, had to say that I have always remembered his analysis of important astrometric problems with admiration. Nine years after the Flagstaff Conference, I find it appropriate to open this Symposium in referring to Schwarzschild's lecture and in presenting my views on recent developments and on progress which I expect in the future.

At the invitation of the Copenhagen University Observatory, 32 workers in the field of meridian astronomy participated in the sessions.

Recent absolute and differential observations of fundamental stars have indicated the need for a revision of the fundamental reference system represented by the positions and proper motions of the FK4. The revision of the FK4 will be based on modern fundamental and differential observations of high accuracy which allow (a) the extension of the FK4 to fainter stars, (b) the improvement of the system, (c) the derivation of individual corrections to positions and proper motions, and (d) the determination of the equinox and its motion. The completion of the programme, resulting in the FK5 and a Supplement giving data in the system of FK5 for bright stars and faint objects (including optical counterparts of radio sources), may be expected about 1980.

Since 1950 about 150 observational catalogues have become available which may contribute to the improvement and extension of the FK4. Twenty-five of these have been classfied as ‘absolute’ or ‘quasi-absolute’ by their authors. Part of the observations, however, are not yet available in publications or in a form suited for data processing. Some of the absolute observations in R.A. suffer from insufficient determination of the azimuth and others in Decl. from unclear elimination of flexure. Main deficiencies in the system of the FK4 are inaccurate positions and proper motions in right ascensions south of − 35°.

The recompilation of PFKSZ (Zverev and Polozhentsev, 1958) catalogue is undertaken in connection with a number of new observations of FKSZ stars which are now available.

About 45 000 absolute and semi-absolute observations of right ascension of the FK4 stars were obtained during 1963–1972. The observations were made with the three instruments of the Cerro Calán Observatory jointly by Chilean and Soviet astronomers. As a result, systematic δαδ cosδ errors were found to exist in the FK4 catalogue. For the reduction of star observations according to the SRS program, it is necessary to derive the system of the δα corrections for the FK4.

It is proposed that transit observations on the islands of Spitsbergen (φ = 78°) and Ross (φ=− 78°) be organised in order to determine absolute right ascension by observing continually throughout the polar night.

The stars in the southern hemisphere with the best observational history in meridian work have been identified and listed at Leiden according to their positions in the sky. Variable and double stars and all stars with |b|10° were omitted. The work could be carried out only for the section from 0h to 16h right ascension. The criterion for good observational history was either to have eight or more catalogue entries in the GFH, or to have five or more entries in the Hamburger IdS.

The observational programs for the Southern Reference Star Program are rapidly drawing to a close. Observations have been completed, except for a few at San Juan and a small percentage of zone −52° to −64° at the Cape. The Cape zone −64° to − 90° has been cancelled. The current state of the observations is shown in Table I.

The AGK3R Catalogue and the FK4 observations made in connection with this catalogue were examined for magnitude effects. Each observatory's observations were compared to the mean position for all stars. A comparison was also made with the stars grouped by spectral type. The magnitude effects found were very small.

Résumé. On examine le problème de l'obtention des mouvements propres à partir des observations meridiennes effectuées dans différents Observatoires, en vue de la détermination de la précision que l'on peut attendre de ces résultats.

The astrometric observations made at the Cerro Calán observatory with several instruments since 1962 are outlined. The resulting catalogues are in press or approaching publication, and are described in some detail. An account is given of the observational projects currently in progress.

The various catalogues are combined in order to demonstrate the large and well-determined systematic differences in Δαδ cosδ between the Cerro Calán observations and the FK4. It is concluded that the FK4 system requires some improvement if it is to fulfil the requirements of a fundamental reference system in the southern hemisphere.

Preliminary results obtained from 6 years of declination observations are presented. Some instrumental details are discussed, and the observed declination system is compared with FK4 in Δδδ.

A total of 110000 observations of 26000 stars was obtained between 1967 and 1972. The internal mean errors are 0″.17 and 0″.27 in Δα cosδ and Δδ, respectively, both multiplied by the factor (cosz)−0.5 at the zenith distance z. The preliminary evaluation also shows that the internal systematic errors, judged from the clamp corrections in 5° zones in declination, are less than ± 0.″02 and ± 0.″15, respectively. The systematic differences in right ascension from the FK4 are given.

The astronomers C. Merfield, J. Moroney, G. Wootthouse, J. Feely and W. Holmes of the Melbourne Observatory made a large series of observations of fundamental stars with the 8″ meridian circle (Troughton and Simms) during 1928–1941. After closing the Observatory all the materials concerned with this large work (about 20000 observations in δ and 30000 observations in α) were forwarded to the Mount Stromlo and then the Pulkovo Observatories for the final reduction and publication (Tavastsherna, 1963).

The potentialities of astrolabe observations which are available for improving the fundamental system, particularly in the southern hemisphere, are discussed. Difficulties arise because of the poor distribution in latitude of the observing stations and diversity of observational programmes.