I have the feeling that to most astronomers the Sun is rather a nuisance. The reasons are quite complex. In the first place the Sun at once halves the astronomer’s observing time from 24 to 12 hours, and then during most of the rest of the time it continues its perversity by illuminating the Moon. Furthermore I have met numerous astronomers who regard solar astronomy to be now, as always before, in a permanent state of decline - rather like Viennese music or English cricket. Nevertheless those who study the Sun and its planetary system occasionally make significant contributions. There were, for instance, Galileo and Newton who gave us mechanics and gravitation; Fraunhofer who gave us atomic spectra; Eddington and Bethe who pointed the way to nuclear energy; and Alfvén who gave us magneto-hydrodynamics. Perhaps the point to be recognized is that the Sun has more immediately to offer to physics rather than to astronomy. That is why it is quite rare that a solar man finds himself with a large captive audience of mainline astronomers: and so the responsibility weighs heavily on my shoulders tonight.

When I was young theoretical cosmology was more a series of exercises in geometry than a branch of astrophysics. Moreover these exercises were based on little more than the Hubble law of red shifts and a general impression that on a large scale the Universe was roughly homogeneous and isotropic. Now all that has changed. While geometrical considerations retain their importance through the dominant role played by general relativity, cosmology has also become highly astrophysical. As a result we can now say a great deal about the early stages of the Universe. My aim is to give a brief account of our present understanding of this fascinating subject, at the same time highlighting the most important problems that remain.

Some of the most striking recent discoveries about interstellar matter involve molecules. It has been known for a long time that there are atoms and ions in space - mainly hydrogen and helium, of course - but also heavier elements like sodium and calcium. In addition, there are solid particles of dust, about 10-5cm across, which must be composed of heavier elements, as hydrogen and helium cannot condense under interstellar conditions.

In 1972, the Orbiting Astronomical Observatory-3, which employs an 80-cm telescope at wavelengths between 1000Å and 3000Å, was launched in the United States and put into operation. In the ensuing year, it has demonstrated that much of the interstellar medium is composed of hydrogen molecules. This result, based upon the observation of Lyman-band absorption in the spectrum of early-type stars, had been anticipated by a rocket observation of H2 by Carruthers in 1970.

The same OAO-3 instrument observed resonance lines of many cosmically abundant elements, and found that these elements often appear to be less abundant in interstellar space than in the solar system, relative to hydrogen. As young stars born recently from the interstellar medium do not show this effect, the heavy elements must in fact be present in some other form. Here I will argue that the heavy elements are largely locked up in the form of the dust and, further, that dust is critical for the formation of the molecules in interstellar space.

It is appropriate that the Orbiting Astronomical Observatory-3 which made these discoveries has been named in honor of Copernicus, the Polish astronomer we honor here on the 500th anniversary of his birth. Just as his discoveries were revolutionary for the understanding of the solar system, those made using the Observatory named in his honor have been revolutionary for the understanding of the Galaxy.

Our Extraordinary General Assembly is devoted to the memory of one of the greatest men of science to the genial Polish astronomer - Nicolaus Copernicus. The main service of Copernicus which has made his name immortal was in finding the correct interpretation of the planetary motions we observe. Instead of geocentric notions, which proved unable to explain the accumulated bulk of empirical data on the apparent motions of planets he has put forward and advocated the notion of a solar system thus presenting the true picture of the part of the Universe we live in. The scientific revolution started by him was continued by Galileo and Kepler and was crowned with the great theoretical generalizations of Newton. As a result a foundation has been created for the most exact theories of motions in the solar system which were developed during the next centuries. These theories in their modern form give also the possibility to solve all the problems concerning the orbital motions of spaceships.

At this stage we can not yet boast that in the study of nuclei of galaxies and their activity we have reached the level which existed in planetary astronomy even before the works of Newton. Only 15 years elapsed from the moment when the idea of activity of nuclei of galaxies was clearly formulated (Ambartsumian, 1958). During these years discoveries of the greatest importance have been made. New unexpected discoveries occur almost each year. These discoveries influence decisively our notions on the diversity of objects and phenomena in the distant space, but they are still insufficient for the construction of adequate theories. In order to penetrate into the very nature of nuclear phenomena we require new observations, new measurements and new data. And if some optimists imagine that the time has already ripen to build a general theory of these phenomena, the more cautious astronomers would like to consider a more or less satisfactory systematization of observational data concerning the activity of nuclei and the understanding of external physical processes accompanying it as a tremendous success.

It was close to the northernmost coast of Europe, in the city of Toruń, that the King of Poland and the Teutonic Knights signed and sealed the peace of 1466, which made West Prussia part of Polish territory. And it was in that city, just seven years later and precisely 500 years ago, in 1473, that Nicholas Copernicus was born. We know relatively few biographical facts about Copernicus and virtually nothing of his childhood. He grew up far from the centers of Renaissance innovation, in a world still largely dominated by medieval patterns of thought. But Copernicus and his contemporaries lived in an age of exploration and of change, and in their lifetimes they put together a renewed picture of astronomy and geography, of mathematics and perspective, of anatomy, and of theology.

When Copernicus was ten years old, his father died, but fortunately his maternal uncle stepped into the breach. Uncle Lucas Watzenrode was then pursuing a successful career in ecclesiastical politics and in 1489 he became Bishop of Varmia. Thus Uncle Lucas could easily send Copernicus and his younger brother to the old and distinguished University of Krakow. The Collegium Maius was then richly and unusually endowed with specialists in mathematics and astronomy; Hartmann Schedel, in his Nuremberg Chronicle of 1493, remarked that “Next to St. Anne’s church stands a university, which boasts many eminent and learned men, and where numerous arts are taught; the study of astronomy stands highest there. In all Germany there is no university more renowned in this, as I know from many reports.” At the university the young Nicholas embraced the study of astronomy with a passion found only in the most exceptional of undergraduates. There he learned about the works of Sacrobosco, Regiomontanus, Ptolemy, and Euclid.

The discovery by Giacconi and his colleagues of variable X-ray sources in close binary systems certainly ranks as one of the highlights of astronomical research during the last 3 years. These remarkable objects have already been extensively studied, by optical and radio observations as well as in the X-ray band; and they seem likely to prove as significant and far-reaching in their implications as pulsars.

The ‘Third Uhuru Catalogue’ (Giacconi et al., 1973a) contains about 160 sources, of which about 100 lie in our Galaxy. Their distribution over the sky (together with other arguments) suggests that these sources have luminosities of the general order 1036–1038 erg s−1, and that their typical distances are ˜ 10kpc. These galactic sources generally display rapid variability. Little else is known about most of them, but they are probably of the same general class as systems such as Her X1, Cen X3, Cyg X1 and Cyg X3. These sources have been investigated in detail, and in all cases one infers a system where the X-ray source is orbiting around a relatively ordinary star. Six sources have been optically identified, and there are some others whose binary nature is established by the occurrence of an X-ray eclipse. Orbital periods range from 4.8 h (Cyg X3) up to ˜ 10 days.

It is a pity for all of us that Dimitri Mihalas was unable to come to Sydney, and I wish, in the first place, to thank him for suggesting this discussion, devoted to a prospective study of our research field. There falls to me the task of trying to sketch what might be the axis of progress in stellar atmosphere theory. This subject is preeminently one which belongs to D. Mihalas; I am afraid that we are going to miss him now more than ever. Furthermore, I feel myself in a bad position for talking on such a large subject, in front of specialists, while I know so little on it. However, I have accepted the task, at the request of the President of Commission 36, with the goal of giving some physical considerations that may initiate reflections and discussions.

I am not going, in principle, to give a set of topics whose study should be desirable, or possible, arranged according to the internal logic of a specialist of stellar atmospheres, neither shall I look for bibliographical signs allowing the prediction of active zones or flares in our next cycle of activity!

The title of this talk is, of course, a bit absurd since no one in his right mind can possibly predict what will happen in the future over even one year let alone ten. However nothing is impossible for Dick Thomas and having accepted his invitation to present this talk I have to pretend to have a crystal ball and put up a good front. I think that the best way to proceed would be to look at the past few years in observational stellar atmospheres and point out some of the highlights, especially those advances which seem to hold great promise for our understanding of stellar atmospheres in the future. The observer’s work falls neatly into two categories: the collection of data and their subsequent interpretation. The former involves the development and use of instrumentation (usually some type of spectrograph with a photon detection system); the latter is so closely linked to theory that it would be impossible to discuss it without recourse to theoretical assumptions and results. Therefore I would like to first mention a few instrumental developments which I consider to be of great importance and then discuss briefly some of the problems to which they might be applied in the next several years.

Exactly a decade ago an international conference on solar physics took place in Utrecht on the occasion of the late Prof. Minnaert’s 70th birthday. Since then, much has happened. Many new instrumental devices were developed or refined. Completely new observational techniques were applied in the XUV and radio wavelengths and in particle detection.

This all resulted in an explosion of new data. Moreover new problems appeared of course. It also resulted in an explosion of papers on solar physics. Actually many more contributions appear than reasonably can be absorbed by the periodical Solar Physics, of which the first volume appeared in 1967. At that time the editors were not at all sure that they would receive enough papers to maintain such a journal. But were there major problems solved recently?

At first I would be inclined to think that, notwithstanding the enormous efforts spent in solar physics, little has been achieved and no spectacular breakthroughs have been found. This impression, probably shared by many more colleagues, becomes stronger if one tries to find a line of progress in ‘classical’ problems of solar physics. We still do not have a satisfactory theory of the Sun’s differential rotation and the Sun’s outer convection zone. One may argue that this is due to our bad knowledge of the interior structure which is not accessible to direct observation. Solar activity and the formation of sunspots is now believed to be a direct consequence of differential rotation and cyclonic convective motions and therefore suffers from the same uncertainties.

The last two decades have been exceptionally fruitful for astrophysics. Because of very rapid developments, especially in the area of observational astrophysics, our view of the Universe has been substantially completed, challenged and altered. Solar Physics has very much been part of this progress. Developments in space and ground-based technology have virtually completely opened up the entire spectrum of solar electromagnetic and corpuscular radiations. Electromagnetic radiation of the sun can now be studied from gamma ray wavelengths shorter than 10-4 Å to radio wavelengths as long as 1014 Å, a range of approximately 60 octaves. Continuing improvements of spatial resolution of the Sun at all these wavelengths and concommitant development of our theoretical understanding of both the radiative and magneto-hydrodynamic processes on the Sun have made solar physics an exciting field to those interested in the Sun per se, as well as to those who view the Sun as a star whose study aids us in the understanding of astrophysics in a broader sense.

A committee of The National Academy of Sciences in the United States under the chairmanship of J. L. Greenstein conducted between 1969 and 1971 a study of the needs of astronomy in the next decade. I took part in this study and it is probably because of this that I was asked to give this review on the next decade in observational solar physics. This review is therefore partly based on the results of the discussions in that committee and in its solar panel. Most of this review will reflect, however, my own opinions.

After reviewing observations of the spectral solar features originated either in the chromospheric layers or in the photospheric layers, from the point of view of the observations, and after having shown the strikingly discrepant set of interpretations that can be found currently in literature, a numerical experiment is performed in a case not too different from the solar case. It is shown that the use of the line bisector to determine, from the asymmetry of a single line, the trend of the velocity field might be considerably misleading, a fact which explains partly the results published in literature.

From an evalution of the arguments pro and contra changes in the precessional constants it is concluded that corrections should be made simultaneously with changes in the values of planetary masses at the time when the new fundamental reference system, the FK5, is introduced into the ephemerides. In this case the location and motion of the equinox would be corrected at the same time. An IAU decision on changes in the constants should be made in 1976. Since the completion of the FK5 may be expected around 1980, the introduction into the ephemerides appears practicable in 1984.

It is well known that the knowledge of precession and nutation is essential for the computation of astronomical coordinates and the comparison of values obtained at different dates. It is therefore important to compute the nutations from the best available observations.

Unfortunately, there are not many long series of reliable observations that can be used for the calculation of the several nutations. Nowadays, we need more accurate values and, therefore, it is fundamental to have observations reduced in an homogeneous way. For this purpose, Commission 19 (Rotation of the Earth) set up a ‘Working Group on Pole Coordinates’, during the last IAU meeting in 1970 (Vicente, 1972), with the objective of reducing the 70 years of variation of latitude observations done by the International Latitude Service (called the International Polar Motion Service at the present time) that constitute a remarkable set of astronomical data. It is expected to obtain more reliable values for the coordinates of the pole and be able to calculate the nutations.

The Working Group on Pole Coordinates is transferring to punched cards all the observations registered in the original observation books and that involves nearly 2 million cards. This work has been hampered by financial difficulties, but it should be supported by the international astronomical community in order to obtain the best results from so many years of observations, done by international cooperation.

The theoretical researches done in the last decades have shown that the values of the nutations depend on the structure of the Earth (Jeffreys and Vicente, 1957). Lately, the researches done in seismology have resulted in a better knowledge about the structure of the Earth, leading to the setting up of many Earth models due to the availability of computers. This fact has led to the situation where one cannot propose better theoretical values for the nutations because they depend on the model adopted for the structure of the Earth.

At the present time the planetary ephemerides in the Astronomical Ephemeris and in the American Ephemeris and Nautical Almanac (both hereinafter referred to as the AE), the Astronomical Ephemeris of the U.S.S.R. and most other national almanacs have the following basis: For Mercury, Venus, Earth, and Mars the general theories of Simon Newcomb (1898a), the ephemeris of Mars including the empirical corrections determined by Ross (1917); for the five outer planets, the numerical integration of Eckert et al. (1951); the Connaissance de Temps publishes ephemerides of Mercury, Venus, Earth, and Mars based on the theories of Leverrier (1858, 1859, 1861a, b); for Jupiter, Saturn, Uranus, and Neptune the ephemerides are based on Leverrier’s (1876a, b, 1877a, b) expressions as modified by Gaillot (1904,1910, 1913). The ephemeris of Pluto is based on the numerical integration of Eckert et al. In all of the above publications the ephemeris of the Moon is now based on the Improved Lunar Ephemeris which is derived from the theory of Brown (1919). Newcomb’s theories and the numerical integration of the orbits of the five outer planets all rest primarily on the system of astronomical constants and planetary masses adopted at the Paris conferences of 1896 and 1911 {Monthly Notices Roy. Astron. Soc., 1912).

As I have already reported (Trans. IAU XVA, 9, 1973), the Working Group on Units and Time-scales was not able to reach any firm conclusions on whether the concepts of the astronomical unit and ephemeris time should be retained or replaced by the SI unit of length (metre) and atomic time. This disagreement was not unexpected as the membership was deliberately chosen to cover a wide spectrum of opinion. The following comments and suggestions represent a middle-of-the-road approach that is intended to meet the requirements of most astronomers and others who use the astronomical data. It has been suggested to me that this approach is not appropriate for use in those precise applications where relativistic concepts are necessary, and that therefore we should abandon completely the use of astronomical units of mass, length and time. There are, however, many applications where Newtonian concepts are perfectly adequate, and astronomical units are widely in use because of their general suitability and convenience. We should therefore continue to define a system of astronomical units, but should state quite clearly their relationships to SI units. An individual may use either system according to the circumstances, and standard conversion factors will be available for use by those who prefer the other system.

This paper reviews results obtained in a program of high resolution infrared spectroscopy of K and M giants. The reported results include (i) a preliminary analysis of the C, N and O abundances for α Ori, (ii) determinations of the 12C/13C and 16O/18O ratios for α Ori (12C/13C ~ 6 and 16O/18 ~ 500), (iii) the derivation of a lower limit, 16O/18O≳ 300, for the 160/18O ratio in α Boo, (iv) a discussion of observations of the SiO first-overtone vibration-rotation bands in M stars, and (v) a search for the fundamental quadrupole vibration-rotation lines of H2.

Current interest in stellar evolution is concentrated on the life of a star after it has left the main sequence. Of particular interest are the red giant or supergiant periods during the hydrogen and helium shell burning phases. Convective mixing during these stages can mix nuclear processed material to the surface where it may be viewed by spectroscopic methods. It is imperative that this rare chance to view processed material be exploited fully to increase our knowledge of stellar evolution.

The observation and interpretation of cool star spectra has its own particular set of problems and advantages. A particular difficulty is the formation of molecules at the low temperatures which occur in the atmospheres of late stars. Not only must the particularly complex spectra of molecules be dealt with but the problem of chemical equilibrium in the atmosphere must be solved accurately before quantitative analysis may be performed. The formation of molecules, however, has one advantage in that it very dramatically separates those stars with carbon to oxygen ratios greater than one from those with ratios less than one. It is the very high dissociation energy of 11.1 eV for the CO molecule which performs this separation. If carbon is less abundant than oxygen all of the carbon is tied up in CO and only oxides are formed in the stellar atmosphere which produce typical M star spectra. If, however, carbon is more abundant than oxygen then carbon compounds such as C2 are formed in place of the oxides and a carbon star spectrum is formed. One of the great advantages of infrared stellar spectra is that it is the only ground based technique for observing CO in stellar atmospheres.