Book contents
- Frontmatter
- EDITOR'S PREFACE
- PREFACE
- Contents
- LIST OF ILLUSTRATIONS
- CHAPTER I BELIEFS AND SUPERSTITIONS RELATIVE TO COMETS
- CHAPTER II COMETARY ASTRONOMY UP TO THE TIME OF NEWTON
- CHAPTER III THE MOTIONS AND ORBITS OF COMETS
- SECTION I COMETS PARTICIPATE IN THE DIURNAL MOTION
- SECTION II MOTIONS OF COMETS
- SECTION III IRREGULARITIES IN THE MOTIONS OF COMETS
- SECTION IV THE ORBITS OF COMETS
- SECTION V THE ORBITS OF COMETS COMPARED WITH THE ORBITS OF THE PLANETS
- SECTION VI DETERMINATION OF THE PARABOLIC ORBIT OF A COMET
- CHAPTER IV PERIODICAL COMETS
- CHAPTER V PERIODICAL COMETS
- CHAPTER VI THE WORLD OF COMETS AND COMETARY SYSTEMS
- CHAPTER VII PHYSICAL AND CHEMICAL CONSTITUTION OF COMETS
- CHAPTER VIII PHYSICAL TRANSFORMATIONS OF COMETS
- CHAPTER IX MASS AND DENSITY OF COMETS
- CHAPTER X THE LIGHT OF COMETS
- CHAPTER XI THEORY OF COMETARY PHENOMENA
- CHAPTER XII COMETS AND SHOOTING STARS
- CHAPTER XIII COMETS AND THE EARTH
- CHAPTER XIV PHYSICAL INFLUENCES OF COMETS
- CHAPTER XV SOME QUESTIONS ABOUT COMETS
- I ELLIPTIC ELEMENTS OF THE RECOGNISED PERIODICAL COMETS OF THE SOLAR SYSTEM
- II GENERAL CATALOGUE OF THE ORBITS OF COMETS
- Plate section
SECTION IV - THE ORBITS OF COMETS
Published online by Cambridge University Press: 05 March 2012
- Frontmatter
- EDITOR'S PREFACE
- PREFACE
- Contents
- LIST OF ILLUSTRATIONS
- CHAPTER I BELIEFS AND SUPERSTITIONS RELATIVE TO COMETS
- CHAPTER II COMETARY ASTRONOMY UP TO THE TIME OF NEWTON
- CHAPTER III THE MOTIONS AND ORBITS OF COMETS
- SECTION I COMETS PARTICIPATE IN THE DIURNAL MOTION
- SECTION II MOTIONS OF COMETS
- SECTION III IRREGULARITIES IN THE MOTIONS OF COMETS
- SECTION IV THE ORBITS OF COMETS
- SECTION V THE ORBITS OF COMETS COMPARED WITH THE ORBITS OF THE PLANETS
- SECTION VI DETERMINATION OF THE PARABOLIC ORBIT OF A COMET
- CHAPTER IV PERIODICAL COMETS
- CHAPTER V PERIODICAL COMETS
- CHAPTER VI THE WORLD OF COMETS AND COMETARY SYSTEMS
- CHAPTER VII PHYSICAL AND CHEMICAL CONSTITUTION OF COMETS
- CHAPTER VIII PHYSICAL TRANSFORMATIONS OF COMETS
- CHAPTER IX MASS AND DENSITY OF COMETS
- CHAPTER X THE LIGHT OF COMETS
- CHAPTER XI THEORY OF COMETARY PHENOMENA
- CHAPTER XII COMETS AND SHOOTING STARS
- CHAPTER XIII COMETS AND THE EARTH
- CHAPTER XIV PHYSICAL INFLUENCES OF COMETS
- CHAPTER XV SOME QUESTIONS ABOUT COMETS
- I ELLIPTIC ELEMENTS OF THE RECOGNISED PERIODICAL COMETS OF THE SOLAR SYSTEM
- II GENERAL CATALOGUE OF THE ORBITS OF COMETS
- Plate section
Summary
Kepler's Laws: ellipses described around the aim; the law of areas – Gravitation, or weight, the force that maintains the planets in their orbits– The law of universal gravitation confirmed by the planetary perturbations – Circular, elliptic, and parabolic velocity explained; the nature of an orbit depends upon this velocity – Parabolic elements of a cometary orbit
What is the nature of a true cometary orbit? In other terms, what is the geometrical form of curve which a comet describes in space–what is its velocity–how does this velocity vary– and what, in short, are the laws governing the movement of a comet?
In order to reply to these questions, and to enable them to be clearly understood, we must first call to mind a few notions of simple geometry, and also the principal laws which govern the motions of the planets.
Kepler, as we have already said, discovered the form of the planetary orbits, hitherto supposed to be circles more or less eccentric to the sun. This great man demonstrated that the form of a planetary orbit is actually an ellipse, that the sun is at one of the foci of the curve, and that the planet makes its complete revolutions in equal periods of time, but with variable velocity ; in fact, that in equal intervals the elliptic sectors described by the radius vector directed from the sun to the planet are of the same area.
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- The World of Comets , pp. 69 - 82Publisher: Cambridge University PressPrint publication year: 2010First published in: 1877