The period of this Report includes 1984 January 1, the date which was probably the most drastic caesura in the history of astronomical almanacs. It seemed, therefore, appropriate to concentrate here to the general aspects rather than to describe the works going on at the particular almanac offices. It is, however, hoped that the past years with their developments and changes will be followed by a period of consolidation and continuity. This would be also of great benefit for the users of the almanacs who still need some time for getting accustomed to so many innovations.

The report period 1982-84 was characterized by an again increased volume of material processed in data and abstracting centers, and by a growing clientele particularly of online services. The Working Groups of Commission 5 seek continued consultation with research object commissions so that the advanced documentation technology be efficiently employed toward specific demands of subject areas as to indexing, tagging, comprehensive, selective and inter-discliplinary retrievals. The guideline library for these purposes has been augmented by the First Dictionary of the Nomenclature of Celestial Objects by A. Fernandez, M.-C. Lortet and F. Spite (Astr. Astrophys. Suppl. 52 no.4, 1983) and by the Guide to the Presentation of Astronomical Data by G.A. Wilkins (CODATA Bull.46 1982); a new draft of the IAU Style Manual is before the IAU EC.

The bulk of the Commission’s work has, as in previous years, been carried out most efficiently by the I.A.U. Bureau, especially by its Director, Dr. B.G. Marsden.

Celestial Mechanics has undergone, in the past three years, a considerable development that has been marked by a significant increase of published papers and by the recent organization of several specialized colloquia or symposia. The reasons of this increase of interest may be found among the following circumstances:

1. - The discovery of new dynamical situations in the Solar system: ellipticity of ringlets, shepherd satellites.

2. - The increase of interest in the problem of the dynamical evolution of the solar system or of its subsystems.

3. - The present necessity to include relativistic effects in the theory of motion of celestial bodies.

4. - New promising results in the analysis of the properties of dynamical systems.

The president thanks those members contributing material to this report. The volume of the material necessitated some editing, but no substantive omissions occurred. Whenever available, AAA numbers are used in lieu of complete titles of publications to help conserve space.

IAU Symposium No. 109 Astrometric Techniques, was held in Gainesville, Florida in January 1984. Although the Proceedings of that meeting are not now available (January 1935), ccmnission members and other interested parties are urged to secure access to that voline when it appears since so many facets of the commission’s work are addressed therein.

Between the Patras and New Delhi General Assemblies no meetings were directly sponsored by Commission 9 because the discipline was amply covered by the following:

• - “Eighth Symposium on Photoelectronic Image Devices,” Imperial College (London) 5-7 September 1983 (B. L. Morgan, Ed., Academic Press, London, 1984).

• - “Advanced Technology Optical Telescopes II” Imperial College, 5-7 September 1983.

• - “Instrumentation in Astronomy V” 7-9 September 1983 (A. Boksenberg and D. Crawford, Eds., Proc. SPIE 415).

• - IAU Symposium No. 109: “Astrometric Techniques,” 9-12 January 1984, Gainsville (Florida).

• - “Astronomical Photography 1984,” Edinburgh, 4-6 April 1984 (E. Sim and K. Ishida, Eds., Number 14 of Occasional Reports of the Royal Observatory, Edinburgh).

• - “IAU Colloquium No. 79: “Very Large Telescopes, Their Instrumentation and Programs,” Garching bei München, 9-12 April 1984 (M. H. Ulrich and K. Kjär, Eds.)

In preparing the present report, which covers the period July 1, 1981, to June 30, 1984, close collaboration has taken place between Commissions 10 and 12, the two solar commissions, in order to avoid duplications and to insure that pertinent subjects are treated. The reader is referred to the report of Commission 12 for further solar topics. It is a pleasure to acknowledge the excellent work of the reviewers who wrote the different sections of this report, and all the members of the commission who provided information on research to be included.

Work begun during the Solar Maximum Year (SMY) (1980-1981) was the focus of several sympsoia and workshops starting in March 1981 with the International SMY Workshop in Simferopol, Crimea (Obridko 1981). Results of the Annecy SMY Workshop (Annecy, France, October 1981) were presented in May 1982 with later work presented at the first SMY symposium (ĸvestka et al. 1982) in Ottawa, Canada. A special symposium for the Study of Travelling Interplanetary Phenomena was held in Maynooth, Ireland, in August 1982 (Shea et al. 1984). Another SMY workshop was held in November 1983 in Kunming, China (Chen 1984), and the second SMY symposium was held in June 1984 in Graz, Austria (Simon 1985). The scientific progress of the SMY is detailed in the above-mentioned publications and in the 1982 U.S.-Japan Seminar “Recent Advances in the Understanding of Solar Flares” (Kane et al. 1983). Highlights of the work of the SMY’s Flare Build-Up Study, Study of Energy Release in Flares, and Study of Travelling Interplanetary Phenomena are presented below.

The ongoing research carried out by the solar community has been reported in the proceedings of several recent symposia, seminars and workshops, as well as in scientific journals (Kane et al. 1983, Švestka et al. 1982a, Shea et al. 1984, Kundu S Woodgate 1984, Simon 1984). We summarize here some of the novel results with reference to flare research as far as SMM data analysis is concerned. Understanding of impulsive phase phenomena was one of the primary goals of the SMM. The early reports from the analysis of the first ever obtained high-resolution images in the <30 keV energy range stressed the fact that some flares showed hard x-ray (HXR) bright sources at the feet of coronal loops (Hoyng et al. 1981a, b, Machado et al. 1982, Duijveman et al. 1982), the so-called HXR “footpoints,” favoring the thick-target beam mechanism for the production of HXRs, and indicating acceleration efficiencies >20% during the early impulsive phase. This phenomenon was shown to be accompanied by soft x-ray (SXR) line broadening, indicative of strong turbulence, and the immediate appearance of blue shifted spectral lines, which shows that plasma heated to >10-1 K rises from the footpoints of loops with velocities to 300 km s-1 (Antonucci et al. 1982, Antonucci et al. 1984a). This result provides a strong indication of the chromospheric evaporation phenomenon, which has been confirmed in analyses of combined SXR and Ha observations (Acton et al. 1982, Gunkler et al. 1984).

Hinotori observed 720 flares through its operation February 1981-October 1981. General discussions of the results were given in two symposia: the Hinotori Symposium (ISAS 1982) and the U.S.-Japan Seminar (de Jager & Švestka 1983). The hard x-ray imaging made at the effective energy 20-35 keV showed a wide variety of morphology. Many flares (22 out of 30 events) showed single source structure, either compact (12) or extended (10) in the spatial resolution of 15 arc sec (Takakura et al. 1983a, Ohki et al. 1983, Takakura 1984). Evidences are given in some limb events that the main source is located in the high corona (1-4 x 104 km) (Takakura et al. 1983b). The extended single source could be the whole coronal loops which may include footpoints, but the maximum brightness is near the loop top. In some events (8 out of 30), weak subsource(s) which sould be identified with the footpoint(s) appear intermittently (Tsuneta et al. 1983). Takakura et al. (1984) found that the extended single source becomes compact and slightly shifts to higher altitudes in later phases of the impulsive burst (5 out of 10 events). Tanaka (1984), Takakura (1984), and Tanaka S Zirin (1984) argued that the hard x-ray morphology of the impulsive burst is consistent with the non-thermal electron beam model in high density corona. Sakurai (1983) investigated magnetic field structures of the hard x-ray sources based on the potential field calculations. Timing between the hard x-ray and microwave in the impulsive bursts was examined by Takakura et al. (1983c), who found correlated subsecond time structures and also by Takakura et al. (1983d), who found a long (5-10 s) delay of the peaks at 17 GHz and E > 300 keV to the peak at E < 100 keV. Kurokawa (1983) showed detailed coincidence between the hard x-ray spikes and Hα brightenings.

Several proceedings of scientific meetings on sunspots appeared during the 1981-1984 period [The Physics of Sunsots, Cram and Thomas (eds.) 1981; see also reports of regional meetings, e.g.. Third European Solar Meeting, Oxford 1981; Nordic Astronomy Meeting, O. Hauge (ed.), Oslo 1983; 11th Regional Consultation on Solar Physics, L. Dezsö and B. Kalman (eds.), Debrecen 1983]. New interest in sunspots was aroused through observations of EUV sunspot spectra from space and was also inspired by the growing number of observations of starspots and other stellar activities [IAU Symposium No. 102, Solar and Stellar Magnetic Fields: Origin and Coronal Effects, J.O. Stenflo (ed.) 1983; Colloquium IAU No. 71 Activity in Red Dwarf Stars, Catania 1982]. Other reasons for the increased interest in sunspots and their energetics were prompted by the correlation between sunspot occurrence and the variations of the solar constant (Hudson et al. 1982) and by the use of sunspot positions for determining solar differential rotation and its change with latitude, depth, and time (Howard et al. 1984, Godoli S Mazzucconi 1982, Balthasar et al. 1984, Tuominen & Kyrolainen 1982, Adam 1983, Koch 1984).

The past 3 years since the last solar maximum have witnessed an unprecedented number (>200) of published scientific papers on many aspects of solar radiophysics. These contributions are the result of an intense research effort mounted during the first Solar Maximum Mission of 1980 and continued until the present. Excellent x-ray, EUV, and visible light observations of the disturbed corona and transition region have been obtained from the SMM, Hinotori, P78-1, and ISEE-3 spacecraft. ISEE-3 also has provided very low-frequency radio observations of solar bursts in the interplanetary medium. Ground-based radio support for space experiments has been provided by many observatories throughout the world. In particular, many collaborative studies using x-ray and radio observations of solar flares have been reported. The outstanding radio instrument during this period has been the VLA, operating at 2, 6, and 20 cm with a time resolution of 10 s and both modes of circular polarization. The two-dimensional spatial resolution of the radio images is a few seconds of arc, almost as good as the best resolution obtained so far at any wavelength in the solar spectrum. To complement the rather poor time resolution of the VLA one-dimensional arrays such as the WSRT at 6 cm wavelength and the Nobeyama interferometer at 17 GHz have been used successfully. In addition, a number of very-high-time resolution radiometers have been built at different locations. At meter wavelengths two-dimensional arrays at Clark Lake, Culgoora, and Nancay and a one-dimensional array at Nobeyama have been employed. The little known region of the solar spectrum at decimeter wavelengths is being investigated by the Zurich spectrograph. It is pleasing to see Chinese participation in solar radiophysics.

The corona above active regions is now recognized as an assemblage of magnetically confined loops of plasma. This advance in understanding the active upper atmosphere is documented in the monograph resulting from the Third Skylab Workshop (Solar Active Regions, 1981, ed., F.Q. Orrall). International collaborative programs during the Solar Maximum Year (SMY) have further stimulated the study of active regions with emphasis on the search for the underlying causes of solar flares. Scores of analyses of individual regions, combining space- and ground-based observations, have been published. We have as a result an improved picture of interactions between active regions: from creation of shear in the magnetic topology to inter-region connections via the corona. A revived interest in the phenomena of recurrent active regions and sunspot decay has highlighted a basic problem for solar magnetism: the removal of magnetic flux from the solar surface. The interpretation of temporary dips in the solar irradiance caused by active regions continues to generate lively debate.

Magnetohydrodynamic (MHD) theory for the initiation and development of solar flares has developed considerably over the past 3 years and represents one of the liveliest areas of solar physics (Hood & Priest, 1981a, Priest 1983a, b, Schindler 1982, Van Hoven 1982, Syrovatskii et al. 1983). This has been stimulated by a thorough analysis of the Skylab observations and also by the startling new observations from the Solar Maximum Mission (SMM). In addition, the realization that flares appear to form two basic types, namely, small simple-loop flares and large two-ribbon flares, has focussed the imagination of theorists (e.g.. Priest 1981, 1982), even though reality may be somewhat more complex. In the former type, a single-loop structure brightens up and decays without moving; whereas in the latter, an active region filament erupts and then two ribbons of chromospheric emission form and separate, with an arcade of hot and cool loops joining them.

The scope of Commission 12 has broadened somewhat in recent years, to include not only the structure of the solar atmosphere, but that of the solar interior as well. The scientific purview of this commission, and of the present report, are complementary to those of Commission 10 (solar activity). Rather than attempting to review all progress in solar structure studies over the past triennium, this report deals with six topics of great current interest, in which there is a great deal of current work.

The study of solar rotation using the Doppler effect in solar spectrum lines continues to be an active and fruitful area of research. Duvall (1982) has confirmed a slower rotation rate for the photosphere than for sunspots, which bears on an earlier controversy regarding this point between the Stanford Solar Observatory and some other observatories. The issue is not settled, however.

During the period 1981-1984, major developments have been made in the analysis of the shape and shifts of photospheric lines used as a diagnostic of the convection in the outer layers of the Sun. The first three-dimensional numerical simulation of the solar granulation has been developed, and it, is able to reproduce with some success most of the observed morphological and spectroscopic properties of granulation. It is becoming clear that the properties of the solar granulation are variable over the solar cycle. Many questions remain to be solved; further progress will rely heavily on expected improvements of the spatial resolution of the observations and the availability of larger computers.

One of the more interesting aspects of the chromosphere-corona transition region is its tendency to exhibit large Doppler shifts. Both the non-thermal velocity component of line widths and the velocity displacement of line positions tend to maximize at temperatures near 105 K. The increase in velocity amplitudes with increasing temperatures below 105 K is readily understood in terms of the increasing sound speed and decreasing densities associated with the outwardly increasing temperature. Why the observed velocity amplitudes should decrease at still higher temperatures is not at all clear, however, and it seems very likely that this phenomenon is indicative of fundamental differences in the dynamics of the upper transition region and corona from those in the lower transition region and chromosphere.

Recent texts dealing with background aspects of this topic include Priest (1982), Noyes (1982) and Giovanelli (1984). Here we concentrate on the equilibrium structure of coronal loops, their oscillations and instabilities, and their heating.