CELESTIAL MECHANICS Volume I Dynamical Principles and Transformation Theory CELESTIAL MECHANICS Yusuke Hagihara VOLUME I Dynamical Principles and Transformation Theory The MIT Press CAMBRIDGE, MASSACHUSETTS, AND LONDON, ENGLAND Copyright © 1970 by The Massachusetts Institute of Technology Designed b;• Dwight E. Agner. Set in Monotype Baskerville. Printed and bound in the United States of America by The Maple Press Company. All rights reserved. No part of this book may be reproduced in any form or by any means, electronic or mechanical, including photocopying, recording, or by any information storage and retrieval system, without permission in writing from the publisher. ISBN 0 262 08037 0 (hardcover) Library of Congress catalog card number: 74-95280 Preface The rather ambitious aim of the present series is to recapitulate the results of the whole field of celestial mechanics and the associated branches of science during the last hundred years. During this period the classical method of formal expansion into series, due to Laplace and Le Verrier, has been severely criticized; a new class of orbits called periodic solutions has been introduced, with applications to Hill's lunar theory. The trig onometric series employed in the ordinary perturbation theory are expanded in powers of the small quantities characteristic ofactual natural bodies, and with arguments proportional to time. Bruns and Poincare have proved that such series are not uniformly convergent, although the existence of the solution has been established on function-theoretic grounds by Sundman. The newly discovered class of functions called "quasi-periodic" and "almost periodic" can be expanded in similar but uniformly convergent form. The question naturally arises: What condi tions should be satisfied by the equations of motion of the n-body problem? There has been some endeavor to solve these equations by resorting to integral equations and infinite nonlinear analysis. The question of stability of motion, especially of the solar system, has been discussed by means of the linearized system of equations according to the ideas of Poincare and Liapounov. The problem is to study stability behavior by means of nonlinear equations, even by dealing with non convergent expansions in the vicinity of the equilibrium point. Birkhoff has extended the idea of periodic solutions of Hill and Poincare to recurrent motions, central motions, and wandering motions, on the basis of measure theory. Another important aspect of the modern trend in celestial mechanics is the topological theory initiated by Poincare and VI PREFACE Birkhoff, for example the invariant-point theorem and the ergodic theorem. The present series ofv olumes undertakes the program oft reating all such questions, extending over the whole of celestial mechanics and associated fields, and of giving suggestions for future development of the subject, stimulated by the launching of artificial celestial bodies. This first volume presents introductory dynamical principles as Part I, and trans formation theory as Part II. Part I begins with the principles of analytical dynamics. From the variational principle of Hamilton, and using the calculus of variations, we deduce Hamilton's canonical form of the differential equations. As an introduction to the topological study ofd ynamical trajectories, Riemann ian geometry is described as it pertains to the quadratic form of the kinetic energy. The notions ofinvariance, covariance, and contravariance are introduced for use in dealing with the canonical transformations. The Hamilton-Jacobi partial differential equation is derived both from the canonical equations and from a hydrodynamical analogy. Liouville's and Stackel's theorems are proved, and the condition for separability of the variables in the Hamilton-Jacobi equation is obtained by using Riemannian geometry; the theorems obtained are also applied to the Schrodinger equation in wave mechanics. Chapter 2 deals with quasi-periodic motions. We define a libration, a revolution, and an asymptotic motion for a simple integrable dynamical system; these definitions serve as keys to much more complicated types of motion in celestial mechanics. The multiply periodic motions and conditionally periodic motions are discussed on the basis of Weierstrass's preparatory theorem in the theory of functions of many variables and Kronecker's theorem in number theory. The motion of molecules in a cubic vessel is solved as a concrete example of ergodicity. Bohl's quasi periodic functions and Bohr's almost periodic functions are defined, and certain of their properties which will be useful later are stated. Schwarzschild's relativistic one-body problem in the gravitational field and the problem of the motion of an earth satellite under the action of the distorted earth are solved by using the Hamilton-Jacobi equation and quasi-periodic motions. Various other methods of treating such problems are subjects of the subsequent volumes. The theory of algebraic integrals is briefly sketched as an introduction to the ideas used in the text. Chapter 3 is dedicated to particular solutions of the three-body and many-body problems. Euler's and Lagrange's types ofp articular solutions are obtained for the n-body problem in a general manner, and the nature of the motion is fully analyzed. The isosceles-triangular solution is discussed on the basis of the theory of analytic functions. PREFACE Vll Part II of this volume begins in Chapter 4 with Lie's theory of con tinuous groups of transformations, with application to the n-body prob lem. The theorems due to Poisson, Liouville, and Lie are proved on the basis of Lie's ideas of complete systems, involution, Lie's function groups and distinguished functions; then these theorems are applied to the integrals of the n-body problem. Integral invariants and adiabatic invariants are introduced for the theoretical reduction of the order of the differential equations. The existence of adiabatic invariants is proved in a general abstract space for use in later arguments. A summary of the modern theory of Lie groups is given with a view to suggesting a new trend of development. In Chapter 5, the differential equations of the n-body problem are reduced by using the known integrals. By Lagrange's, Levi-Civita's, and Poincare's transformations, the differential equations are reduced to the lowest order. The two-body problem, especially, is discussed in full; and various expansions are obtained, using the theory offunctions as applied to Keplerian motion to establish the convergence of the expansions. Then the equations for the variation of elements, Delaunay's, Poincare's, and Kepler's, are derived as the fundamental principle in perturbation theory. The role of the angular-momentum integral .is stressed in view of the elimination of the node by Jacobi. Various kinds of canonical variables are defined, along with their dynamical meanings. Chapter 6 is devoted to discussions ofBruns's and Poincare's theorems. The generality ofBruns's proof of the theorem of the nonexistence of new algebraic integrals is extended from three bodies to n bodies. The proof of Painleve's extension of Bruns's theorem is given. The integrals of the restricted three-body problem are discussed with special reference to the ergodic theorem. Poincare's theorem concerning the nonexistence of new uniform integrals is proved and discussed in full detail. Exceptions to Poincare's theorem are also dealt with. The top motions of Euler, Lagrange, and Kowalewski are discussed from the point of view of Bruns's and Poincare's theorems, and the solution, given with integrals, is based on the theory of algebraic functions, especially on the Riemann 0-functions and the hyperelliptic functions. Volume II, which will be published shortly after Volume I, will contain perturbation theories in classical celestial mechanics for the motions of planets, asteroids, satellites, comets, and the moon, that is, theories of Laplace, Lagrange, Delaunay, von Zeipel, Hansen, Gylden, Hill, Brown, and others, and their applications to the motions of artificial celestial bodies. Questions will be raised on the gaps in the asteroidal distribution and on the capture of comets. Vlll PREFACE In Volume III, the form of the solutions of these perturbation theories and the convergence of the series expansions for the solutions will be discussed on mathematical grounds. The question of the third integral of motion will be touched upon. Differential equations with periodic co efficients and with quasi-periodic coefficients will be used in connec tion with perturbation theory. Krylov-Bogoliubov's averaging method and Diliberto's periodic surface theory will be applied to the motion of celestial bodies. In Volume IV, Poincare's theory of periodic solutions will be discussed in full with various modern versions of the theory and with practical applications to the three- and many-body problems. Periodic solutions will be dealt with on the basis ofWintner's nonlinear infinite analysis and Lichtenstein's nonlinear integral equations. Motions in the neighborhood of an equilibrium point will be discussed according to the theories of Birkhoff and Siegel. The conditional existence of quasi-periodic solutions in the manner of Kolmogorov, Arnold, and Moser will be shown. The stability theory of Liapounov and its modern development will be described. Volume V will contain proofs of the existence of the solution of the three-body problem by Sundman, Levi-Civita, Chazy, and Merman, as well as the proofofthe rigorous capture theory of Merman; finally, there will be discussed the topological theory of Poincare and Birkhoff, including the theory of characteristics, manifolds of motion, surface transformations, the invariant-point theorem, the ergodic theorem, and almost periodic motions. The author wishes to express his appreciation for a unique editorial collaboration: Dr. Peter Musen of the National Aeronautics and Space Administration's Goddard Space Flight Center (GSFC) kindly read the manuscript and offered aid and encouragement as the work progressed. Subsequently, Dr. Musen gave generously of his time and wisdom to Mr. R. L. Tanner, chief editor of GSFC, and his associate Mr. P. Barr, who with NASA support jointly prepared the work for the publishers. Yusuke Hagihara Tokyo, July 1968