The two years that elapsed since the establishment of Division 1 have been characterised by a large variety of tasks of common interest to the five Commissions forming the Division. This is shown in particular by the activity of the Working Groups on Astronomical Standards (Chairman, T. Fukushima) and on Reference Frames (Chairman, L.V. Morrison) which include members from the five Commisions and were actually Division 1 Working Groups. This is also reflected by the very close relationship that prevailed between Commissions 8 and 24. They actually are preparing an eventual merging between the two commissions by proposing that both commissions have the same Vice-President for the next term (E. Schilbach). Last, but not least, three of the Joint discussions accepted for the Kyoto General Assembly are sponsored by the whole Division, one of its Commissions being the proposer. However, these common actions are only a small fraction of the activity of each Commission as described in their reports.

During 1994-1996 Ephemerides have been intensively developed for all celestial bodies in the solar system in both analytical and numerical ways, except an analytical ephemeris of Pluto. Because of the shortage of allotted pages this report covers only the reviews of planetary ephemerides. Ephemerides of natural satellites and other bodies will be included in the next report as six years' achievements. Conventional reports from institutions and individual members were published in the Newsletter of Commission 4.

In preparing this report the reviews by M. Standish and P. Bretagnon are highly appreciated.

The time period covered by this report (1 July 1993 - 30 June 1996) has seen the flawless launch and operation of SOHO, the full development of the Global Oscillation Network (GONG) and other seismology networks, a continued successful operation of YOHKOH, the southern and northern passages of ULYSSES, as well as significant advances in high resolution solar observing techniques.

The topics of the present report have been chosen with the aim to maintain a long-term balance in the coverage of activities of the three Commissions, ranging from instrumentation and observing techniques to the most important work and new scientific results from studies of the Sun and Heliosphere. It is our intention to provide critical reviews of the field, which may also be useful for the non-specialist reader.

Spatial structures in the solar photosphere are likely to be seen down to scales of the order of the photon mean free path, which is about 70 km in the lower photosphere. This scale corresponds to an angle of O.”1 at disk center. Structures associated with magnetic fields may be expected on even smaller scales. Existing solar telescopes typically have diameters of slightly less than one meter. Hence, even in the visible part of the spectrum, the scales of solar structures extend out to the diffraction limit of current solar telescopes. Therefore, the achievable spatial resolution is limited by turbulence in the Earth’s atmosphere (seeing). This has led to the development of various techniques to overcome this resolution limit and achieve diffraction-limited resolution. This report covers selected highlights and recent work done in the context of high-resolution techniques published in the period from July 1, 1993 to June 30, 1996. Due to the lack of space the report remains necessarily incomplete, and I apologize to all the authors of important contributions that are not cited here. This review does not cover space and balloon-borne instruments that try to achieve high spatial resolution by observing from above the Earth’s atmosphere. Recent work on ground-based high-resolution techniques has been collected in the proceedings of the 13th Sacramento Peak Summer Workshop on Real Time and Post Facto Solar Image Correction (Radick 1993).

Solar wind ion composition measurements are a unique tool to investigate solar system processes, ranging from the solar interior out to the heliospheric boundary. Compositional changes in the solar wind, which originates in the outer convective zone (OCZ) of the Sun, are produced in the transport of solar matter from the OCZ to the solar corona and in the process of lifting the coronal plasma out of the solar gravitational field up to the termination shock and beyond. During the last three years instrumentation originally designed to measure the composition of the solar wind has detected further pick-up ion species in the solar wind and thereby strongly motivated pick-up ion related research. This review therefore puts particular emphasis on pick-up ion observations and their theoretical interpretation.

This report has, following the usual practice in Commission 15, been compiled primarily by the chairpersons of the two working groups. E. Tedesco prepared the entire section about Asteroids and Meteorites. H. U. Keller prepared the section about Comets using material originally prepared by E. Kiihrt (nuclei), H. Bohnhardt (dust), R. Schulz (neutral gas), and W.-H. Ip (plasma). M. F. A’Hearn did minor editing to merge the two reports and fit the report into the allotted space.

This report includes a number of achievements in planetary science in the last approximately three years. Each section was contributed by the scientists identified at the end of that section.

In the past triennium, the output of the Commission continued its explosive growth within a rather broad range of activities. In comparison with the previous triennium (which also saw impressive growth), the current period witnessed a 26% increase in the number of numbered minor planets (7041 minor planets), a 46% increase in the number of minor planet orbits computed (14 154) and a 187% increase in the number of optical Minor Planet observations (260 616). In addition, there were 65 radar Doppler and time delay measurements made during the triennium bringing the total to 269 observations of 40 minor planets and 5 comets.

The light of the night sky is a difficult to disentangle mixture of tropospherically scattered light, airglow, zodiacal light (including the thermal emission by interplanetary dust particles), unresolved stellar light, diffuse scattering and emission by interstellar dust and gas, and finally an extragalactic component. It has the reputation of being a very traditional field of astronomy, which certainly is true if we look at the long history of the subject. The recent renewed interest in this topic, which continued during this triennium, appears mainly to come from three sources: - first from the impressive results of the IRAS and COBE infrared satellites. They brought to general consciousness the fact that the infrared sky is characterised by strong emission from interplanetary and interstellar dust, and made clear that this emission may interfere with the study of faint interesting sources. - then from the development of sensitive detectors and arrays for essentially all of the wavelength range to be covered in this report, from the Lyman limit to ≈ 300 μm. Now the difficult measurements of the ultraviolet diffuse radiation and of the extragalactic background light in the infrared cosmological windows around 3 μm and 200 μm have become feasible and state of the art projects. - finally, the threat to astronomical observations arising from man-made development and lighting has become important enough to further studies of uncontaminated and contaminated night sky brightnesses. This report will refer mainly to those areas and is meant to highlight noteworthy developments. It was prepared with the help of Drs. Bowyer and Mattila.

As has been the usual practice for a number of years in Commission 22, members of the commission with expertise in different areas have prepared contributions reviewing their own fields and these have been consolidated by the President and Secretary to form the report as it appears below. Over the past triennium there have been a number of conferences and meetings concerned either solely with meteors and/or interplanetary dust or include these subjects amongst the topics covered, in fact too many, especially in the latter category, to list in detail. Many of the papers referenced below are from the proceedings of those conferences and these proceedings may also contain other papers, not specifically referenced in the reviews, that may nevertheless be of interest to commission members.

The past three years have been extraordinarily productive for the Bioastronomy community. In particular, the detection of extrasolar planets and the possible evidence for fossil life on Mars have given substance to the concept of life elsewhere in the universe, and reinforced the connection between life on Earth and its cosmic origin. The structure of this report follows the agenda from the highly successful IAU Colloquium 161 on Bioastronomy, organized by Cristiano Cosmovici and Stuart Bowyer on the island of Capri in July 1996. The content has been provided by attendees of that Colloquium. Given the breadth of the subject matter covered by this Commission, this report could not have been generated any other way, and I am most grateful to all the contributors.

At the 1988 Baltimore General Assembly of the International Astronomical Union, members of several Commissions dealing with planetary science expressed deep concern that no work was being undertaken to identify and avoid pollution problems in interplanetary space beyond the Moon. At that time NASA had convened a conference on problems in cislunar space due to the large and growing numbers of orbiting fragments hazardous to space vehicles. In translunar space this is hardly a problem. However an alarming number of future interplanetary mission proposals were considered for other reasons to be potentially harmful to various solar system bodies and interplanetary space itself.

The Divisions’s Organizing Committee is made up of the Presidents and Vice-presidents of these commissions and their immediate past-Presidents. By a process as yet unexplored by historians, I was asked to serve as President of the Division. Owing to a personality trait well known to psychologists, I agreed to serve! Division IV, which was formed at the last General Assembly, comprises five commissions: