Classical methods of compiling catalogues of proper motions from catalogues of positions at different epochs and reduction to a rigorously defined homogeneous coordinate-system are reviewed, and the determination of proper motions of numerous stars by photographic differential methods, partly with assumptions on behaviour of faint reference stars, and partly by attachment to reference frames of stars with proper motions known from catalogues is discussed.

At Lick the second phase of the proper motion program is in progress. In addition to generally selected stars, as was done for the first phase, so far over 30000 stars of special types of astro-physical interest and about 29000 AGK3 stars have been selected for measurement.

In accordance with the Pulkovo program, second-epoch photography with galaxies is being continued at Pulkovo, Moscow and Tashkent, and proper motions with reference to galaxies are derived.

Analyses of proper motions at Pulkovo and Lick show agreement in some instances and disagreement in others. The same applies to comparisons with fundamental catalogues. The analyses suffer to some extent from absence of proper motions in the zone of avoidance and in the southern part of the sky.

In the southern hemisphere, first-epoch photography of 164 fields with galaxies has been completed using the Maksutov double-meniscus telescope at Cerro El Roble in Chile, and a complete coverage of the sky has been started with the same telescope; this work is being done jointly by the Soviet and Chilean astronomers. On the Yale-Columbia southern program, the first-epoch photography is nearly completed with the double astrograph at Leoncito in Argentina. There are plans at Lohrmann Institute, Dresden, to take photographs with the 2-m Schmidt telescope at Tautenburg, thus providing first-epoch plates for proper motions with reference to galaxies.

This program is best introduced by saying that it constitutes the southern counterpart of the well known Lick proper motion program. In fact, it has been designed to be almost identical to that so that when the work on the materials from both hemispheres has been completed, a homogeneous set of data will be available for the entire celestial sphere.

The secular parallaxes, determined by Klemola and Vasilevskis from proper motions of stars relative to galaxies (Klemola and Vasilevskis, 1971), were interpolated in latitude for each area of the Pulkovo Catalogue (Fatchikhin, 1974). Then the mean values were grouped in three zones of galactic latitude (b) and the data obtained at the Lick Observatory (L) were compared with our data (P) (Fatchikhin, 1972, 1973). The results are given in the Table I.

In Photographic Astrometry the absolute proper motions of stars are determined relative to galaxies by the direct (I) or indirect (II) methods. In the direct method the plate constants are determined directly from galaxies, used as the reference stars with a Zero proper motion. In the indirect method the proper motions are first found relative to the totality of reference stars Sr (r=1, 2,… r0), then the obtained relative proper motions are reduced to absolute values by means of galaxies Gg (g = 1,2,… g0), the correction, identical for all the stars, being derived by formula (I).

The fully inherent information of the AGK 2 plate material, covering the northern hemisphere down to δ= −2.5° with homogeneous epoch and limiting magnitude has not been used to establish the AGK2 catalogue. A new measurement will provide positions for all stars with at least mpg=2 in the FK4 system, yielding an estimated accuracy of σ = 0″.14.

In March 1973 a newly developed zone astrograph for the yellow spectral-region has been set in operation at the Hamburg observatory which would be available about 1975 for a new fourfold coverage of the northern hemisphere. A technical description of the instrument is given. Details of the fourfold plate coverage and the observing program are discussed. As a suitable reference star system the AGK3R catalogue, updated with recently derived proper motions to that epoch, is adopted. A final positional accuracy σ = 0″.11 of the new catalogue is expected. The available epoch difference of 45 years up to that date will then provide proper motions in the FK 4 system with an estimated accuracy of at least 0″.005/a for all stars of the northern hemisphere down to mpg=2.

A method of analysing proper motions as observed over all the sky is described. The kinematics of nearby stars derived from the Lick Pilot Survey are discussed, and the consequences to galactic structure examined.

First results of the Herstmonceux programme of redetermination of proper motions in the Selected Areas are presented. Plate material includes the old Radcliffe plates, old plates taken at Greenwich and modern plates taken on the 26-in. refractor at Herstmonceux. The plates are being measured on GALAXY and reduced according to the plate-overlap technique.

From a comparison between the rotational velocities derived from radial velocities and space motions of OB stars, large systematic errors of FK4 proper motions in the southern hemisphere are evaluated; these may be expected, from the known accuracy of the FK4. The error of adopted distance scale is also examined. It is suggested that meridian observations of OB stars should be extended to the southern hemisphere to further researches, not only on stellar kinematics, but also on the fundamental system.

It is shown by means of several examples, that the visual observations of the relative rectilinear motion of components of wide optical double stars can be used to estimate the precision of catalogue proper motions.

(1) Astronomical refraction is one of the oldest astronomical problems, which has been investigated many times, but the existing knowledge of refraction is not sufficient to meet modern requirements for accurate astrometric data. The present investigations cast light on several facts which might help the advancement in the calculation of astronomical refraction.

(2) There are several questions concerning the calculation of the astronomical refraction, from the laws of refraction to meteorological factors. These difficulties have prevented the development of a satisfactory refraction theory for a long time, leading to the conservation of old methods, but the accuracy of the refraction determinations has not increased. We are using old refraction theories and tables based on them for the most part, while the anomalous refraction is not considered. Seeing that the calculated refraction values are not acceptable, we are determining the formal refraction corrections directly from astrometric measurements, but these corrections are not real from the physical point of view.

The present uncertainty in the calculated refraction is of the order of 0″.01, increasing with zenith distance. For observations near the horizon the existing refraction theories cannot give acceptably accurate values.

(3) The greatest progress in the knowledge of refraction influences would be achieved if instead of mean meteorological data we could use direct measurement. There are some propositions of this kind.

The new refraction tables are in preparation. We are very careful in taking into consideration the local characteristics and the correct calculation of the chromatic refraction.

Frankly speaking, we must say that it is practically impossible to calculate a real influence of refraction and for this reason certain precautions are advisable. A careful positioning of the instrument may simplify the density field and thus eliminate the greatest part of the anomalous refraction. But the best proposition is to observe at small zenith distances only, not larger than 45° if possible.

(4) Our conclusion is that, in current astrometric practice, we must continue refraction investigations and in addition to the refraction at optical wavelengths, it is absolutely necessary to investigate the radio and laser-refraction too.

The first results of a planned continuing investigation of astronomical refraction are reported in this paper. Pure and anomalous refraction are investigated using meteorological data and environmental models. Numerical methods based upon Chebyshev polynomials are developed. Applications are made to Winslow, Arizona (which is somewhat similar to El Leoncito, Argentina), and to results of PZT observations made in Washington, D.C.

The successful improvements of meridian instrumentation during the past twenty years have mainly come through electronic devices and computers being applied for facilitating the data handling and for increasing the accuracy. Photographic recording of the circle and of the star has played an important role here, but has for both tasks gradually lost its attractiveness as direct photometric-electronic methods have become available. At the same time new types of the telescope system have been introduced without convincing results as yet, but this field still holds promises for the near future.

The problems of the refraction, the meridian building, the foundation of the instrument and the site selection have been treated in recent years and these efforts will be doubly repaid when the telescope and micrometers become more nearly perfect. Altogether, it need not be long before a few partly automatic instruments produce observations with a mean error of 0″.15 and a systematic error of 0″.03 at a rate of 300 observations per observing night. In addition the limiting magnitude can be mv = 11 or 12, thus 2 mag. fainter than for visual observations. These goals are conservative – most of them have already sometimes been surpassed – and they should be compared to a present day good visual meridian circle giving a mean error 0″.30, a systematic error 0″.10 and 120 observations per night.

The relative roles of meridian and photographic astrometry must be defined anew in the light of the great improvements of both methods.

The instrumental constants of the Naval Observatory's Automatic Transit Circle are discussed in conjunction with the transit circle's on-line data acquisition and control system. The reflecting collimators have been designed with CerVit primaries and minified point sources. The mark lens configuration is comprised of a long focal length lens and wedge manufactured from a single piece of fused silica. The on-line data acquisition and control system will permit real time monitoring of these instrumental parameters.

The observations in R.A. with the Pulkovo HMC and investigations of the instrument, reported in Trans. IAUXIVA (p. 39), are being continued during the past two years (Pinigin, 1972, 1973). Some of the new results are as follows:

There are many advantages in having at the same site, a large array of various instruments for astrometry and geodynamics, in particular in order to provide a good insight into the systematic errors of various methods. This is one of the reasons why a new observational center is being equipped now near Grasse. The site chosen is the best found for Danjon astrolabes. It will start its operation in 1974 and will include two astrolabes, a satellite laser, a Doppler satellite receiving station, a Schmidt telescope fit for astrometric observations and, later, a lunar laser and other equipment.

Although several lunar laser ranging stations exist, only one is now fully operational: the McDonald station with internal observational errors of less than 15 cm. The interpretation of the data involves a great number of parameters relative to the Earth and the Moon which are listed.

The lunar laser is particularly fit for those parameters that pertain to the Moon, and with future lasers accurate to 2 or 3 cm, it may be expected that this accuracy will be projected into these parameters. The probable determination of the semi-major axis to 1 cm accuracy for a few months mean would imply a new means of determining the non conservative part of the motion of the Moon. A similar precision is to be expected for the rotation of the Moon. The situation for the Earth parameters (Earth rotation and polar motion) is not so good, because of a rather weak geometry of the problem and the monthly one week gap in the observations. Nevertheless, it will give a very useful external check on other competing methods (radio-interferometry, laser or radio-satellites).

On fait une analyse des différents procédés de mesure des distances dans le système solaire et dans son voisinage en vue de mettre en évidence les différentes corrections que ces mesures peuvent nécessiter.