The many papers by Soviet authors have been translated into English by A. P. Kirillov, N. A. Nikiforova, E. A. Voronov, and others. Some of the papers were trans lated by the authors themselves. The discussion records have been prepared at the Institute for Theoretical Astronomy by V. K. Abalakin, N. A. Belyaev, A. P. Kirillov, V. A. Shor, E. A. Voronov, N. S. Yakhontova, and others. The three papers published in French have been carefully checked by B. Milet. The final editing has been done at the Smithsonian Astrophysical Observatory, and we thank J. H. Clark, P. D. Gregory, J. E. Kervick, and G. Warren for retyping much of the material. Our special thanks are due to the D. Reidel Publishing Company for the excellent care they have taken in printing these proceedings of IAU Symposium No. 45. G. A. CHEBOT AREV E. I. KAZIMIRCHAK-POLONSKA Y A B. G. MARSDEN INTRODUCTION The idea to organize a Symposium on 'The Motion, Evolution of Orbits, and Origin of Comets' dates back to the IAU thirteenth General Assembly, held in 1967 in Prague. Owing to the impossibility of completing during the General Assembly the discussion on the problem of orbital evolution of comets Professor G. A. Chebotarev, then the newly elected President of IAU Commission 20, initiated the organization of the international symposium in Leningrad where the full scope of cometary problems might be considered from the viewpoint of celestial mechanics.

The many papers by Soviet authors have been translated into English by A. P. Kirillov, N. A. Nikiforova, E. A. Voronov, and others. Some of the papers were trans lated by the authors themselves. The discussion records have been prepared at the Institute for Theoretical Astronomy by V. K. Abalakin, N. A. Belyaev, A. P. Kirillov, V. A. Shor, E. A. Voronov, N. S. Yakhontova, and others. The three papers published in French have been carefully checked by B. Milet. The final editing has been done at the Smithsonian Astrophysical Observatory, and we thank J. H. Clark, P. D. Gregory, J. E. Kervick, and G. Warren for retyping much of the material. Our special thanks are due to the D. Reidel Publishing Company for the excellent care they have taken in printing these proceedings of IAU Symposium No. 45. G. A. CHEBOT AREV E. I. KAZIMIRCHAK-POLONSKA Y A B. G. MARSDEN INTRODUCTION The idea to organize a Symposium on 'The Motion, Evolution of Orbits, and Origin of Comets' dates back to the IAU thirteenth General Assembly, held in 1967 in Prague. Owing to the impossibility of completing during the General Assembly the discussion on the problem of orbital evolution of comets Professor G. A. Chebotarev, then the newly elected President of IAU Commission 20, initiated the organization of the international symposium in Leningrad where the full scope of cometary problems might be considered from the viewpoint of celestial mechanics.

The many papers by Soviet authors have been translated into English by A. P. Kirillov, N. A. Nikiforova, E. A. Voronov, and others. Some of the papers were trans lated by the authors themselves. The discussion records have been prepared at the Institute for Theoretical Astronomy by V. K. Abalakin, N. A. Belyaev, A. P. Kirillov, V. A. Shor, E. A. Voronov, N. S. Yakhontova, and others. The three papers published in French have been carefully checked by B. Milet. The final editing has been done at the Smithsonian Astrophysical Observatory, and we thank J. H. Clark, P. D. Gregory, J. E. Kervick, and G. Warren for retyping much of the material. Our special thanks are due to the D. Reidel Publishing Company for the excellent care they have taken in printing these proceedings of IAU Symposium No. 45. G. A. CHEBOT AREV E. I. KAZIMIRCHAK-POLONSKA Y A B. G. MARSDEN INTRODUCTION The idea to organize a Symposium on 'The Motion, Evolution of Orbits, and Origin of Comets' dates back to the IAU thirteenth General Assembly, held in 1967 in Prague. Owing to the impossibility of completing during the General Assembly the discussion on the problem of orbital evolution of comets Professor G. A. Chebotarev, then the newly elected President of IAU Commission 20, initiated the organization of the international symposium in Leningrad where the full scope of cometary problems might be considered from the viewpoint of celestial mechanics.

A comprehensive overview of the extraterrestrial matter that falls to Earth from space.

Pt.2: Flyby missions and systematic observations of comets are projected for studying comet nuclei and cometary dust tail structures.

Meteor Showers and their Parent Comets is a unique handbook for astronomers interested in observing meteor storms and outbursts. Spectacular displays of 'shooting stars' are created when the Earth's orbit crosses a meteoroid stream, as each meteoroid causes a bright light when it enters our atmosphere at high speed. Jenniskens, an active meteor storm chaser, explains how meteoroid streams originate from the decay of meteoroids, comets and asteroids, and how they cause meteor showers on Earth. He includes the findings of recent space missions to comets and asteroids, the risk of meteor impacts on Earth, and how meteor showers may have seeded the Earth with ingredients that made life possible. All known meteor showers are identified, accompanied by fascinating details on the most important showers and their parent comets. The book predicts when exceptional meteor showers will occur over the next fifty years, making it a valuable resource for both amateur and professional astronomers.

The investigation of minor solar system bodies, such as comets and asteroids, using spacecraft requires an understanding of orbital motion in strongly perturbed environments. The solutions to a wide range of complex and challenging problems in this field are reviewed in this comprehensive and authoritative work.