A Short History of Astronomy
By Arthur Berry
1. Astronomy is the science that treats the sun, the moon, the stars, and other objects, such as comets, seen in the sky. It deals to some extent with the earth, but only so far as it has properties in common with the heavenly bodies. In early times, astronomy was concerned almost entirely with the observed motions of the celestial bodies. At a later stage, astronomers could discover the distances and sizes of many of the heavenly bodies and weigh some of them. More recently, they have acquired a considerable amount of knowledge as to their nature and the material of which they are made.
2. We know nothing of the beginnings of astronomy. We can only conjecture how certain of the more straightforward facts of the science—particularly those directly influencing human life and comfort—gradually became familiar to early humanity, as familiar to modern savages. With these facts it is convenient to begin, taking them in the order in which they most readily present themselves to any ordinary observer.
3. The sun is seen daily rising in the eastern part of the sky, traveling across the sky, reaching its highest position in the south in the middle of the day, sinking, and finally setting in the western part of the sky. But its daily path across the sky is not always the same: the points of the horizon at which it rises and sets, its height in the sky at midday, and the time from sunrise to sunset all go through a series of changes, which are accompanied by changes in the weather, in vegetation, etc.; and we are thus able to recognize the existence of the seasons, and their recurrence after a specific interval of time which is known as a year.
4. But while the sun always appears as a bright circular disc, the next most conspicuous of the heavenly bodies, the moon, undergoes changes of form that readily strike the observer and are at once seen to take place in regular order and at about the same intervals of time. A little more care, however, is necessary to observe the connection between the form of the moon and her position in the sky concerning the sun. Thus, when the moon is first visible soon after sunset near the place where the sun has set, her form is a thin crescent (cf. fig. 11 on p. 31), the hollow side being turned away from the sun, and she sets soon after the sun. Next night, the moon is farther from the sun, the crescent is thicker, and she sets later; and so on, until after somewhat less than a week from the first appearance of the crescent, she appears as a semicircular disc, with the flat side turned away from the sun. The semicircle enlarges and, after another week, has grown into a complete disc; the moon is now nearly in the opposite direction to the sun and, therefore, rises at sunset and sets about at sunrise. She then begins to approach the sun on the other side, rising before it and setting in the daytime; her size again diminishes until, after another week, she is again semicircular. The flat side is still turned away from the sun but is now turned towards the west instead of the east. The semicircle then becomes a gradually diminishing crescent, and the time of rising approaches the time of sunrise until the moon becomes altogether invisible. The new moon reappears after two or three nights, and the whole series of changes is repeated. The different forms thus assumed by the moon are now known as her phases; the time occupied by this series of changes, the month, would naturally suggest itself as a convenient measure of time, and the day, month, and year would thus form the basis of a rough system of time-measurement.
Genre: Non-Fiction
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Arthur Berry
I have tried to give in this book an outline of the history of astronomy from the earliest historical times to the present day and to present it in a form that shall be intelligible to a reader who has no special knowledge of either astronomy or mathematics and has only an ordinary educated person’s power of following scientific reasoning.
Biography.
To accomplish my object within the limits of a tiny volume, it has been necessary to pay the strictest attention to compression; this has been effected to some extent by the omission of all but the scantiest treatment of several branches of the subject which would figure prominently in a book written on a different plan or a different scale. I have deliberately abstained from giving any connected account of the astronomy of the Egyptians, Chaldaeans, Chinese, and others to whom the early development of astronomy is usually attributed. On the one hand, it does not appear possible to form an independent opinion on the subject without first-hand knowledge of the documents and inscriptions from which our information is derived. On the other hand, the various Asian scholars who have this knowledge still differ so widely from one another in their interpretations that it appears premature to embody their results in the dogmatic form of a textbook. It has also seemed advisable to lighten the book by omitting—except in a very few simple and essential cases—all accounts of astronomical instruments; I do not remember ever deriving any pleasure or profit from a written description of a scientific instrument before seeing the instrument itself, or one very similar to it. I have abstained from attempting to give my readers what I have never succeeded in obtaining myself. The book’s aim has also necessitated the omission of several significant astronomical discoveries, which find their natural expression in the technical language of mathematics. On this account, I have only been able to describe in the briefest and most general way the beautiful superstructure that several generations of mathematicians have erected on the foundations laid by Newton.
For the same reason, I have been compelled occasionally to occupy a good deal of space in stating in ordinary English what might have been expressed much more briefly, as well as more clearly, by an algebraical formula for the benefit of such mathematicians as may happen to read the book I have added a few mathematical footnotes; otherwise, I have tried to abstain scrupulously from the use of any mathematics beyond simple arithmetic and a few technical terms which are explained in the text. A good deal of space has also been saved by the total omission of, or the briefest possible reference to, a vast number of astronomical facts which do not bear on any well-established general theory. For similar reasons, I have generally abstained from noticing speculative theories that have not been established or refuted. In particular, for these and other reasons (stated more fully at the beginning of chapter XIII.), I have dealt in the briefest possible way with the immense mass of observations via which modern astronomy has accumulated; it would, for example, have been easy to have filled one or more volumes with an account of observations of sun-spots made during the last half-century, and of theories based on them, but I have only given a page or two to the subject.
I have given short biographical sketches of leading astronomers (other than living ones) whenever the material existed and have attempted in this way to make their personalities and surroundings tolerably vivid. Still, I have tried to resist the temptation of filling up space with picturesque details that have no real bearing on scientific progress. The trial of Kepler’s mother for witchcraft is probably quite as interesting as that of Galilei before the Inquisition. Still, I have entirely omitted the first and given a good deal of space to the second because, while the former appeared to be chiefly of curious interest, the latter seemed to me to be not merely a striking incident in the life of a great astronomer, but a part of the history of astronomical thought. I have also inserted many dates, as they occupy very little space and may be helpful to some readers. In contrast, others can easily ignore them to facilitate reference of the dates of birth and death (when known) of every astronomer of note mentioned in the book (other than living ones) that have been put into the Index of Names.
I have not scrupled to give a good deal of space to descriptions of such obsolete theories as appeared to me to form an integral part of astronomical progress. One of the reasons why the history of science is worth studying is that it sheds light on the processes whereby a scientific theory is formed to account for specific facts and then undergoes successive modifications as new facts are gradually brought to bear on it and is perhaps finally abandoned when its discrepancies with facts can no longer be explained or concealed. For example, no modern astronomer as such need be concerned with the Greek scheme of epicycles, but the history of its invention, of its gradual perfection as fresh observations were obtained, of its subsequent failure to stand more stringent tests, and of its final abandonment in favor of a more satisfactory theory, is, I think, a valuable and exciting object-lesson in the scientific method. At any rate, I have written this book with that conviction and have decided very mainly from that point of view what to omit and include.
The book makes no claim to be an original contribution to the subject; it is written largely from second-hand sources, many of which are not very accessible to the general reader. An appendix gives particulars of the authorities used.
I remain grateful to acknowledge the help I have received in my work. Mr. W. W. Rouse Ball, Tutor of Trinity College, whose excellent knowledge of the history of mathematics—a subject very closely connected with astronomy—has made his criticisms of exceptional value, has been kind enough to read the proofs, and has thereby saved me from several errors; he has also given me valuable information about portraits of astronomers. Miss H. M. Johnson has undertaken the laborious and tedious task of reading the whole book in manuscript and proof and verifying the cross-references. Miss F. Hardcastle of Girton College has also read the proofs and verified most of the numerical calculations and the cross-references. To both, I am indebted for the detection of a large number of obscurities in expression, as well as of clerical and other errors and misprints. Miss Johnson has also saved me much time by making the Index of Names, and Miss Hardcastle has rendered me a further service of great value by drawing many diagrams. I am also indebted to Mr. C. E. Inglis of this College for Fig. 81. I have to thank Mr. W. H. Wesley of the Royal Astronomical Society for various references to the literature on the subject, particularly for help accessing multiple illustrations.
I am further indebted to the following bodies and individual astronomers for permission to reproduce photographs and drawings, and in some cases also for the gift of copies of the originals: the Council of the Royal Society, the Council of the Royal Astronomical Society, the Director of the Lick Observatory, the Director of the Instituto Geographico-Militare of Florence, Professor Barnard, Major Darwin, Dr. Gill, M. Janssen, M. Loewy, Mr. E. W. Maunder, Mr. H. Pain, Professor E. C. Pickering, Dr. Schuster, Dr. Max Wolf.
ARTHUR BERRY.
Arthur Berry
