A series of plates is being taken with the U.K. 48-inch Schmidt Telescope at Siding Spring on a field centred on the star GC 1110 near the South Galactic Pole, in order to detect any stars brighter than about mpg = 18, which may have significant trigonometric parallaxes.

A search list of more than 16, 300 objects in an area 4¼° × 4¼° has been formed from a preliminary scan on the Galaxy machine at R.G.O. Prom 1974 January to 1976 January some 30 plates have been obtained, nearly half of which have been measured in each of two orientations on Galaxy; each measuring run takes about 16 hours.

The Observatory of Strasbourg will participate in the future in the general radial velocity survey which is in hand at the Observatories of Haute-Provence and of Marseille with FEHRENBACH’s Objective-prism astrograph. A programme of this type, providing a large number of data, is particularly suitable at the place where the “Data Center” is growing up.

A radial velocity survey is a vast programme which needs many years to be fulfilled. It is natural that one starts with the most interesting areas in the sky, one of them being the area near NGP. In 1976 twenty fields were covered, each by one plate, in that direction. The whole programme covers 70 overlapping fields in an area of 100 square degrees centered at NGP. The limiting magnitude shall be almost the 12th.

The USA Mariner 10 spacecraft encountered Mercury three times in 1974-1975. The 1st and 3rd encounters provided detailed observations of a well developed, detached bow shock wave which results from the interaction of the solar wind. The planet possesses a global magnetic field, and modest magnetosphere, which deflects the solar wind. The field is approximately dipolar, with orientation in the same sense as Earth, tilted 12° from the rotation axis. The magnetic moment, 5×1022 Gauss-cm3, corresponds to an undistorted equatorial field intensity of 350γ, approximately 1% of Earth’s. The origin of the field, while unequivocally intrinsic to the planet, is uncertain. It may be due to remanent magnetization acquired from an extinct dynamo or a primordial magnetic field or due to a presently active dynamo. Among these possibilities, the latter appears more plausible at present. In any case, the existence of the magnetic field provides very strong evidence of a mature, differentiated planetary interior with a large core, Rc ≈ 0.7RM, and a record of the history of planetary formation in the magnetization of the crustal rocks.

It was not generally anticipated by lunar scientists that the Moon rocks would prove to possess a natural remanent magnetization because the absence of a present field had already been demonstrated and it was almost universally believed that the Moon did not possess an iron core in which such a field could be generated. Consequently the initial investigation of Apollo 11 rocks was directed towards the use of rock magnetic studies as an adjunct to petrological examination. One of the most notable findings of the Apollo programme was the demonstration of the existence of a natural remanent magnetization (NRM) in Apollo 11 lavas and breccias. Experiments on the stability of the NRM enabled it to be concluded that the rocks were already magnetized when they were on the Moon. This conclusion was soon corroborated by the discovery of the existence of a steady magnetic field at the Apollo 12 site of the magnitude expected from the intensity of the NRM of about 36 γ (in addition to the field fluctuating solar wind. It was reasoned from this early work that the natural remanent magnetization had been acquired at the time of origin of the rocks or at least in their early history and a case was made out that this was a thermoremanent magnetization acquired as the lava flows cooled from magma flowing into the mare basin and as the high grade breccias cooled after the impacts. The origin of the natural remanent magnetization of the low grade breccias is more problematic and the role of other kinds of remanent magnetization processes has been investigated, particularly the effect of shock.

This is a progress report of a project designed to find the component, perpendicular to the Galactic plane, of the gravitational potential of the Galaxy. The principle is to measure the radial velocities and distances of a large number of K-giant stars near the North Galactic Pole. My student G. A. Radford is masterminding the project; collaborating with us are Drs. J. E. Gunn of the Hale Observatories and L. Hansen and K. Gyldenkerne of Copenhagen.

We have measured the radial velocities of all the HD stars of type KO and later, and many of the G5 stars, within 15°of the Galactic Pole, using the Cambridge photoelectric spectrometer. In addition, we have observed all the stars classified as K giants by Upgren in his declination zones 25° to 31°, using the spectrometer on the Hale telescope. There are about 900 stars observed altogether, including about 200 Upgren stars, running down to twelfth magnitude or so, which are not in the Henry Draper Catalogue. To determine the distances of all these stars we are now trying to determine the absolute magnitudes by narrow-band photoelectric photometry in the Copenhagen system. Most of the observations have been made, thanks largely to the very generous grants of observing time given by the Hale Observatories earlier this year; but the reductions have only been completed for about 300 stars (including 244 K giants) which were observed last year at Kitt Peak, and the present, very preliminary, discussion is based on those stars alone.

A brief descriptive summary of Jupiter’s magnetosphere is based on in situ observations with the spacecraft Pioneer 10 and Pioneer 11 in November-December 1973 and November-December 1974, respectively. Current interpretative work emphasizes particle acceleration and loss mechanisms, the determination of diffusion coefficients by satellite effects, the topology of the outer magnetosphere, the possible recirculation of energetic particles, and the controversial evidence for an extended magnetotail.

Available evidence on non-thermal radio emissions of the planet and on the solar wind flow at 10 AU is invoked to suggest that Saturn very likely has a large, well developed magnetosphere resembling that of Jupiter but with the important difference that a radiation belt can not exist interior to the outer edge of the A ring of particulate matter. The first in situ observations will be made by Pioneer 11 in August-September 1979.

Several Lick 3-m prime-focus plates of Selected Areas 57, 68, and 51 (taken by I. King) in B, V, and R have been measured for stellar magnitudes down to the plate limit by L. Hinrichs and King, and are currently being measured by Chiu for proper motions (several hundred stars per plate) with the Berkeley PDS microdensitometer. Prime-focus plates are also available from the Hale 5-m and Mayall 4-m telescopes, giving an overall baseline of 20 years. Work so far indicates that on the Lick plates stars brighter then V = 19 can be measured to within one micron standard error; the error becomes unacceptably large for stars fainter than V = 20. A large number of stars bluer than B-V =0.4 show proper motion and are therefore excellent candidates for white dwarfs. For 0.4 ≤ B-V ≤ 0.8, the proper motion stars are expected to be predominantly subdwarfs.

The frequency distributions of the stars in V and B-V for the three fields are being analysed by Brooks; the fields are advantageously placed for study of the density distributions in both the disk and the halo. These data should allow the halo stars to be studied out to a distance of 10 to 15 kpc, as well as a determination of the degree of flattening of the halo. Also, a study will be made of the z and ῶ density gradients in the disk, and the luminosity function of disk stars.

Swedish investigations on stellar space distribution generally are based on the Uppsala - Stockholm spectral classification system. In this system the properties of the stars are derived from objective prism spectra by means of narrow-band photometry. The main criteria are the hydrogen-line intensities, the intensity of the K line, the intensity of the G band, the break at the G band, and the intensity of the blue cyanogen band (for a description of the system see e.g. Ljunggren and Oja, 1961), when possible supplemented by a measure of the Balmer discontinuity (Rydström, 1976). The method yields absolute magnitudes with a dispersion of about and intrinsic colours (B-V)° with a mean error below for most kinds of stars.

Three investigations are relevant to the subject of this Joint Discussion.

The landers Venera 9 and 10 transmitted to Earth television pictures of the immediate vicinities of landing sites. The pictures were taken by optical-mechanical panoramic cameras looking from view-ports at about 0,9 meter above the ground. The nominal field of view is 40°x l80°. The width of one element of the picture (camera resolution) is 21 minutes of arc. The pictures were subsequently treated by computer enhancement. The first results of panorama analysis were published elsewhere (1,4).

Venera 9 landed at the point 32°N, 291°E on the rather steep (˜20°) slope covered by angular sharp-edged rock fragments. The fragments have a horizontal dimension of up to 50 or 70 cm, and a vertical dimension of no more than 15 to 20 cm. Some of the fragments demonstrate the evidence of layering approximately parallel to the flattening of fragments. The surface between fragments is darker than the fragment surfaces of the same orientation and seems to be composed mainly of particles of a size less than the resolution of the camera. The on-board gamma-spectrometer reveals that the radioactivity of the surface at Venera 9 site is similar to radioactivity of basaltic rocks of the Earth ( 2 ).

A short account was given of results recently published (Hill et al. 1976; Hilditch et al. 1976a, b) of a spectroscopic and photometric study of 310 A0-F8 stars within 15° of the north galactic pole. Using these data, it has been found that δmo for the programme stars is constant out to 250 pc and corresponds, via Crawford’s (1975) calibration, to the solar value of [Fe/H]. The distribution of radial velocities of A0-F8 stars is asymmetric and may be interpreted as showing a broad distribution of mean −7 kms−1 and dispersion σ ~ 11 kms−1 together with a superposed narrow distribution of mean 0 kms-1 and dispersion σ ~ 3 kms-1. The narrow component originates from a group of 37 stars which appear to be kinematically and spatially associated with the Coma cluster. Only 14 of these 37 stars are recognised members of the Coma cluster. Removal of these 37 stars from the sample results in a distribution which matches closely the W component distribution of A0-F8 stars in Gliese’s (1969) catalogue. Thus Oort’s “well-mixed” hypothesis seems to be confirmed out to 250 pc. Much additional work on the space motions is required before the hypothesis of the ‘Coma group’ can be thoroughly tested. Results of this analysis and a preliminary value for the total mass density in the solar neighbourhood is expected to be completed during the next few months.

Analysis of cratering on all terrestrial planets and satellites has produced tools to study (1) the past meteoroid and planetesimal environment, (2) the erosive environments of planetary surfaces, and (3) the relative and absolute ages of planetary surface units. Important findings include a decline in lunar crater production rate from a value 4 x 109 years ago that was thousands of times higher than the present, to present values which have been relatively constant for 2 to 3 x 109 years; evidence for an erosive period or periods on Mars that degraded many Martian craters but declined substantially at some time in the past; and the concept of destruction of primeval planetary surfaces by early intense cratering and production of a mega-regolith.

Since the time allowed per paper at this joint discussion is short only one aspect of the stellar distribution at high galactic latitudes will be presented here, namely the distribution of field horizontal-branch stars (FHB) in the galactic halo. First, the method by which FHB stars are found will be described. Second, the density distribution of FHB stars will be compared with that of the RR Lyrae stars.

As part of a general program to study the stellar density distribution perpendicular to the galactic plane a number of possible FHB stars has been discovered. In each survey area objective prism plates (at a dispersion of 280 Å/mm. to a limiting magnitude of V = 14) are taken with the Michigan Curtis Schmidt telescope at Cerro Tololo Inter-American Observatory or the Schmidt telescope at the Warner and Swasey Observatory. A set of direct plates are taken also to obtain photographic magnitudes for the stars with spectral classifications.

Pioneer 10 flew by Jupiter in December 1973 and Pioneer 11, in a more polar trajectory, one year later. We present some of the pictures of Jupiter made with the spin-scan technique by the imaging photopolarimeter. The pictures are presented here without comment as a detailed description of Jupiter together with references concerning the instrument and its results, and were published in the book, Jupiter, edited by T. Gehrels (University of Arizona Press, 1976).

Recently Dessureau and Upgren (1975) redetermined the velocity distribution of giant stars in the north galactic pole direction using Upgren’s (1962) catalogue and Oort’s (1960) determination of K(z). The velocities were assumed to be represented by n Gaussian distributions with no further constraints imposed. The velocities are well represented by three such distributions whose properties disagree with those found by Oort. A larger number did not improve the stability of the solution. Without radial velocities, however, they could not redetermine the K(z) force itself.

Data on the surface distribution of galaxies in a number of clusters has been given by several authors (see, for example, Shane & Wirtanen 1954; Zwicky 1956, 1957; Omer, Page & Wilson 1965; Clark 1968; Noonan 1971, 1974; Bahcall 1971, 1972a, b, 1973a, b, 1974, 1975; Rudnicki 1963; Rudnicki & Baranauska 1966a, b; Rood et al. 1972; Rood & Sastry 1972; Oemler 1974; Austin & Peach 1974a, b; Chincarini & Rood 1975, 1976; and references quoted therein). The distributions show a relatively smooth fall-off from a high density at the center of the cluster to a low density tail at the outskirts of the cluster. Secondary maxima or subclustering are sometimes superimposed on an otherwise smooth and monotonic profile.

Stock and Osborn (1972, 1973) have shown that objective-prism spectra taken with a conventional prism may be measured to produce radial velocities of sufficient accuracy for statistical purposes. They are determined by means of a third-order power series in both x and y coordinates. The same spectral-line measures can also yield positions such that proper motions can be determined if first-epoch positions are also available. For many stars, both tangential and radial velocities can be obtained with about the same error which is of the order of ± 20 km/sec. The field distortions caused by the prism are large but are constant and predictable to the degree that measured residuals are similar in size to those for direct images (Stock and Upgren 1968). A survey of a high-latitude zone between −30° and −35° in declination is underway and a catalogue of about 3000 stars has already been compiled by Stock. For each star, the catalogue lists an accurate 1950 position, spectral and luminosity type, apparent photographic magnitude, relative radial velocity and its weight, and the number of plates on which the star was measured.

A matrix method involving eigenvector expansion is used to solve the “fundamental equation” of stellar statistics. This method is applied to M dwarfs and K giants.

Clusters of galaxies are easily identifiable collections of galaxies, all at the same distance and all observed under similar conditions of galactic obscuration, etc. They are, therefore, very convenient samples with which to study the matter content of the universe. However, clusters are also very particular physical environments, and from this latter point of view it is their atypical character which is of interest. The differences in the contents of one cluster from another, and of each from the contents of small groups and the “field” can teach us much about how the properties of galaxies depend on the environments in which they were born and have evolved.

Because of the interrelatedness of these two points of view, one cannot really understand the galaxy populations of clusters until one also understands the populations of galaxies which are not in clusters. Therefore, while this review will concentrate on the contents of rich clusters of galaxies, it will also be necessary to discuss the properties of non-cluster galaxies.