Astronomiske observationer: observatorier, udstyr og metoder

One of the wonderful aspects of the US Manned Spaceflight Program was the opportunity for people around the entire globe to participate in one of man's greatest adventures. As we laid out the plans for flying the first manned spaceflight program, it was obvious that we would require exten- sive operations around the earth. One of the most challenging features of this plan was to build a world-wide network of tracking stations to provide communications with the orbiting spacecraft. At the time, about 1958 and 59, the construction of these facilities, in what turned out to be some very interesting pieces of geography, was a tremendous task. Christopher C. Kroft, Jr. Australia is located roughly 180 degrees longitude from the launch site, Cape Canaveral, and so occupied not only a unique position but a very critical one. Determining the position of the spacecraft as it traversed the Australian continent was critical to the orbit determination. This set of parameters was necessary to properly manage the entire operation. Such things as the time of retrofire, paramount to recovery of the crew, and the information required for signal acquisition at each of the tracking sites around the world are but two examples. Also, because the status of the astronaut and the spaceship were extremely critical to the deci- sion-making process, the stations down under provided vital data to evalu- ate the progress and to allow the flight control team to manage the problems that inevitably developed.

The next major step in millimetre astronomy, and one of the highest-priority items in radio astronomy today, is a large millimetre array with a collecting area 2 of up to 10 000 m . A project of this scale will almost certainly require inter- national collaboration, at least within Europe, and possibly with other major partners elsewhere. In order to establish a focal point for this project within Europe, a study has been undertaken by the Institut de Radio Astronomie Mil- Ii met rique (IRAM), the European Southern Observatory (ESO), The Onsala Space Observatory (OSO), and The Netherlands Foundation for Research in Astronomy (NFRA). In the context of this project, a workshop attended by some 100 participants was held at ESO Garching on December 11-13, 1995 to discuss the scientific advances such an array will make possible. Throughout the three days of the workshop the strong enthusiasm for the concept of a large millimetre array in the southern hemisphere (the Large South- ern Array, or LSA) was obvious, and it became clear that such a facility would have a profound impact on almost all areas of observational astrophysics. It was particularly clear that, since their main science drivers (cosmology, and the origins of galaxies, stars and planets) are the same, and their angular resolutions and sensitivities similar, the LSA and the VLT would strongly complement each other.

At close inspection every galaxy appears to have its own individuality.A galaxy can be warped, lop-sided, doubly-nucleated, boxy or disky, ... in its own specific, peculiar way. Hence, for a complete description, galaxy taxonomy may ask for finer and finer classification schemes. However, for some applications it may be more fruitful to let details aside and focus on some global properties of galaxies. One is then seeking to measure just a few quantities for each galaxy, a minimum set of globalobservables that yet captures some essential aspect of these objects. One very successful example of this approach is offered by the scaling rela- tions of galaxies, the subject of the international workshop held at ESO head- quarters in Garching on November 19-21, 1996. Discovered in the late 1970's, the Tully-Fisher relation for the spirals and the Faber-Jackson relation, or its more recent version the Fundamental Plane, for ellipticals have now become flourishing fields of astronomical research in their own right, as well as being widely used tools for a broad range of astronomical investigations. The work- shop was designed to address three key issues on galaxy scaling relations, i.e., their Origins, Evolution, and Applications in astronomy. The Origins of galaxy scaling relations still escape our full understanding.

The controversial question of whether the majority of the narrow absorption lines observed in QSO spectra represent cosmological intervening systems or ejecta from the QSO themselves is settled. QSO absorption line spectroscopy, initially a mere technique, has matured into an essential extragalactic research tool for understanding the content of the Universe at redshifts between 0 and 4, and beyond. The only previous important meeting devoted to "e;QSO Absorption Lines"e; was held in May 1987 at the Space Telescope Science Institute in Baltimore, Maryland, U.S.A. Since that time, nearly a decade ago, research has been ex- tremely active in this now well-established field of astrophysics. Theoretical stud- ies and simulations have taken advantage of the constant progress in computer technology, and during these last few years, the observational results have bene- fited largely from the new facillities offered by the Hubble Space Telescope in the UV wavelength range and the Keck Telescope for high-resolution spectroscopy.

Jets are ubiquitous in the Universe, but ill-understood. Conservative books base their interpretations on focused stellar winds, ejected "e;bullets"e;, black-hole central engines, and in-situ upgrading of electron energies via shocks. This volume, however, attempts a uniform interpretation of the bipolar-flow family, involving extremely relativistic pair plasma as the jet substance, and rotating magnets (possibly burning disks) as the central engines. Among the discussed sources are SS 433, YSO jets, planetary nebulae, our galactic center, and the class of extragalactic QSOs, both radio-loud and radio-quiet.

It has always been ESO's aim to operate the VLT in an interferometric mode (VLTI) which allows the coherent combination of stellar light beams col- lected by the four 8-m telescopes and by several smaller auxiliary telescopes. In December 1993, in response to financial difficulties, the ESO Council de- cided to postpone implement at ion of the VLTI, Coude trains and associated adaptive optics for all the UTs but included provisions for continuing tech- nological and development programmes devoted to the aim of reintroducing these capabilities at the earliest possible date. The desirability of carrying out the full VLTI programme as originally envisaged at the earliest possible moment has not, however, diminished, es- pecially in view of VLTI's exceptional capabilities and resulting potential for new and exciting discoveries. In recent years, interferometric projects have begun to playa central role in ground-based high-resolution astronomy, and numerous instruments have been completed or are in the process of construc- tion. Several large-aperture interferometers will probably co me on-line near the turn of the century. The impending presence of these new instruments represents an important incentive both for clarifying the scientific cases for various VLTI implementation plans and for ensuring VLTI's competitiveness in the international context over the next 1O~20 years.

The reader will find in this volume the Proceedings of the NATO Advanced Study Institute held in Cortina d'Ampezzo, Italy between August 3 and August 13, 1987 under the title "e;Long Term Dynamical Behaviour of Natural and Artificial N-body Systems"e;. The Institute was the latest in a series held in 1972, 1975, 1978, 1981, 1984 in dynamical astronomy, theoretical mechanics and celestial mechanics under the Directorship of Professor Victor Szebehely. These previous institutes, held in high esteem by the international community of research workers, have resulted in a series of well-received and valuable Proceedings. In correspondence with Professor Szebehely and in long discussions with him in Colorado in August 1985, I agreed to his request that I undertake the preparation of a new ASI. I was happy to do so knowing I could call upon his vast experience in overseeing such ASI's. The last quarter century has been a period in which increasingly rapid progress has been made in celestial mechanics and related subjects not only because of the appearance of new problems urgently requiring solution but also because of the advent of new analytical techniques and powerful computer hardware and software.