In May 1962 the International Union of Theoretical and Applied Mechanics (IUTAM) organized a symposium in Paris on the theory of the movement of the Earth's artificial satellites designated to confront the results of the first spatial experiences with the mechanical point of view. The papers submitted during this meeting have been published in 1963 in a collection entitled "Dynamics of Satellites" by Springer- Verlag. During the last three years the importance of studies pertaining to the dynamics of artificial satellites has continued to increase, and many results due to observations have led to a deeper knowledge of the field of forces in which these objects move, particularly the field of gravitation of the Earth, the forces due to pressure of radiation, friction of the atmosphere, etc ...A new symposium seemed therefore suitable to determine these recent advances. However, this time it appeared appropriate to consider it more from the point of view of the interpretation obtained from the results of observations (determination of orbits and forces existing) than from the point of view of the theory of motion. For this reason the complete title of the second symposium is as follows: "Trajectories of Artificial Celestial Bodies, as Determined from Observations".

After the launching of the first artificial satellites preceding interplanetary vehicles, celestial mechanics is no longer a science of interest confined to a small group of astronomers and mathematicians; it becomes a special engineering technique. I have tried to set this book in this new perspective, by severely limiting the choice of examples from classical celestial mechanics and by retaining only those useful in calculating the trajectory of a body in space. The main chapter in this book is the fifth, where a detailed solution is given of the problem of motion of an artificial satellite in the Earth's gravitational field, using the methods of Von Zeipel and of Brouwer. It is shown how Lagrange's equations can be applied to this problem. The first four chapters contain proofs of the main results useful for these two methods: the elliptical solution of the two-body problem and the basic algebra of celestial mechanics; some theorems of analytical mechanics; the Delaunay variables and the Lagrangian equations of variation of elements; the expansion of the disturbing function and the Bessel functions necessary for this expansion. The last two chapters are more descriptive in character. In them I have summarized briefly some of the classical theories of celestial mechanics, and have tried to show their distinctive characteristics without going into details.

decision and investigative process of the scientist, they can also wri te the paragra}ils of scientific resul ts. Once a canputer research activity progresses from intuitive guesses to a systematic study, the canputer program can free the scientist to pursue new original ideas. '!his concept is illustrated in the ptper by Hut. Sussnan says "Knowledge" is knowing what not to canpute. His main message is that we must change from trying to maximize the efficiency of the canputer to maximizing the effectiveness of the scientist. The canputer is relatively cheap, it is the trained scientist who is most valuable. In the second keynote address, R. L. Duncombe (University of Texas) described the "Early Applications of Canputer Technology to Dynamical Astronany. " His talk traced the worldwide introduction of punched card equipnent and their applications through the use of the first electronic canputers. Sussman and Duncombe, therefore, provided a forecast and review of the use of computers in dynamical astronany. This proceedings is intended to provide a consolidated general view of the ptst, present, and future of the Applications of Canputer Technology to Dynamical Astronany. Of necessity this requires that the ptpers be rela ti vely short and provide references to the more canplete discussions. Thanks to the representa tion from so many different countries the proceedings give a picture of the activities worldwide. The Scientific Organizing Comnittee included K. B. IIlatnagar, V. A. Brtmberg, G. Contopoulos, A. Depri t , J. Henrard, J. Kovalevsky, Y.

This book on reference systems is the first comprehensive review of the problem of celestial and terrestrial reference systems and frames. Over 20 years, the importance of this problem emerged slowly as the accuracy of new observational techniques improved. The topic has already been approached in several symposia such as Stresa (1967), Morioka (1971), Perth (1973), Columbus (1975, 1978 and 1985), Kiev (1977) and San Fernando (1978). Two IAU colloquia held in Turin (1974) and in Warsaw (1980) were exclusively devoted to discuss reference systems. During this time, the problem of terrestrial and celestial reference systems has been discussed also in many astronomical and geodetic symposia, but always among other topics. Thus, a review devoted solely to the definition and practical realization of such systems was needed. It is hoped that this book, containing modern comprehensive reviews of important facets of this problem will contribute not only to a better and wider understanding of the mathematics and the physics that are behind the concepts and the realizations, but also to future development in a field that can only expand with the rapidly increasing accuracy of geodetic and astronomical observations. We are pleased to thank all the authors of the book who have enthusiastically agreed to contribute to the book in their field of competence and have gracefully accepted guidance from the editors in the definition of the subject and of the interfaces with other chapters. We thank Prof. Y.

An introduction to practical astrometry, dealing with the determination of positions, motions, distances and dimensions of celestial bodies ranging from quasars to artificial satellites. For this 2nd edition, the release of the Hipparcos and Tycho catalogs, the rise in CCD astrometry and the adoption of a new celestial reference frame by the IAU led to a significant modification of the text. And, especially, the outlook for astrometry has been completely rewritten.

The book is an introduction to practical astrometry, dealing with the determination of positions, motions, distances and dimensions of celestial bodies ranging from quasars to artificial satellites. The main part is devoted to the description of instruments and observing techniques, and also includes the basic properties of optical instruments and a detailed description of the atmospheric effects on observations. A brief summary of the main phenomena in positional astronomy and of data treatment is given. Although classical astrometric methods are described, emphasis is put on new, more precise techniques such as CCD, optical and radio interferometry, space astrometry, etc. For this 2nd edition, the release of the Hipparcos and Tycho catalogs, the rise in CCD astrometry and the adoption of a new celestial reference frame by the IAU led to a significant modification of the text. And, especially, the outlook for astrometry has been completely rewritten.

The driving idea, in organizing this Symposium on "Relativity in Celestial Mechanics . and Astrometry" was that, in recent years, the ac curacy of several Astrometric techniques has so much increased that re lativistic effects are no more marginally mentioned in academic presen tations but have become an intrinsic part of the interpretation of all the positional data. Techniques such as V. L. B. I., space probes, lunar lasers, etc . . . have greatly contributed to reduce the accuracy level to an angular equivalent of a few milliarc-seconds. HIPPARCOS will extend this trend to stellar astrometry and new proposals aim at gaining ano ther one or two orders of magnitude in observing precision. In paral lel, great progress has also been made in the theories of motion of ce lestial bodies and more rigourous treatments within the frame of general relativity become necessary. The definition of reference frames and of various coordinate times become also a major problem in the intercompa rison of observations produced by different methods. This Symposium gave to people using relativistic corrections in reducing their measurements or in constructing various theories of mo tion a chance to exchange their experience in the field and to confront it with theoreticians in general relativity. The Symposium was approved by the IAU in 1983 and it was organi zed by the Institute of Theoretical Astronomy of the USSR Academy of Sciences on May 28-31, 1985."

Astrometry encompasses all that is necessary to provide the positions and motions of celestial bodies. This includes observational techniques, instrumentation, processing and analysis of observational data, reference systems and frames, and the resulting astronomical phenomena. Astrometry is fundamental to all other fields of astronomy, from the pointing of telescopes, to navigation and guidance systems, to distance and motion determinations for astrophysics. In the last few decades, new observational techniques have enabled improvements in accuracy by orders of magnitude. Starting from basic principles, this book provides the fundamentals for this new astrometry at milli- and micro-arcsecond accuracies. Topics include: basics of general relativity; co-ordinate systems; vectors, tensors, quaternions, and observational uncertainties; determination and use of the celestial and terrestrial reference systems and frames; applications of new observational techniques; present and future star catalogues and double star astrometry. This comprehensive reference will be invaluable for graduate students and research astronomers.

Astrometry encompasses all that is necessary to measure the positions and motions of celestial bodies: observational techniques, instrumentation, processing and analysis of observational data, and reference systems and frames, as well as the resulting astronomical phenomena. It is fundamental to all other fields of astronomy, from the focusing of telescopes to navigation and guidance systems and distance and motion determinations for astrophysics. Starting from basic principles, this work provides the principles of astrometry at milli- and micro-arcsecond accuracies and will be an invaluable reference for graduate students and research astronomers.