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Physics of Comets,Third Edition



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Author: K. S. Krishna Swam

Publisher: World Scientific Publishing Company

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Publish Date: August 26, 2010

ISBN-10: 9814291110

Pages: 460

File Type: PDF

Language: English

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Book Preface

Among the various objects of the solar system, comets have attracted and fascinated the common man to a large extent for the last two thousand years or so. This information comes from the ancient records of paintings or drawings of comets on caves, clothes, etc. as well as from the observations of early writers. It was not until the sixteenth century that comets were demonstrated to be celestial objects. This came from the work of Tycho Brahe who observed the bright comet of 1577 AD with accurate instruments and from various locations in Europe. This really revolutionized the ideas about comets and from then on, observers took a serious view of comets and started making position measurements.

The complete credit for the discovery that comets are part of the solar system goes to Edmond Halley. Halley, using Newtonian mechanics, showed that the comets which had appeared in 1531, 1607 and 1682 are the one and the same with a period of about 751 2 years. He also noticed that the time interval between the successive perihelion passages was not the same. He concluded rightly that this could be due to the perturbation of the cometary orbit produced by the planets Jupiter and Saturn. Following these successes, he predicted that the same comet would return in 1758. As predicted, the comet did appear in 1758, though Halley, dead by then, was not there to witness the glorious triumph of his prediction. This comet is therefore named after him. In recent years this comet has been traced backwards through many centuries by several investigators through orbit calculations. Through this work, it has been possible to identify every appearance of the comet as shown by ancient records until about 240 BC. So far, it seems to have made about twenty-eight appearances.

Since early times, the appearance of a comet has been associated with disasters, calamities, tragedies and so on. One benecial result of such wrong notions and ideas is that the appearances of most comets are recorded. These observations have proved very valuable to modern astronomers. Although there were many bright comets which have been recorded since early times, somehow the Comet Halley seems to have attracted much more attention than the others. The comet which has been depicted in the Bayeux tapestry is the Comet Halley which appeared in 1066 AD (Fig. 1.1). The comet in the tapestry can be seen to hover above the English King Harold who is being told of the bad omen. Such types of association of Comet Halley with the occurrence of bad things on Earth have also been made for many other apparitions. The last apparition of Comet Halley in 1910 drew wide publicity (Fig. 1.2). It was very bright and enormous in extent. Actually the Earth passed through the tenuous gas of this comet’s tail.


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