THE MOON A FULL DESCRIPTION AND MAP OF ITS PRINCIPAL PHYSICAL FEATURES doc

THE MOON A FULL DESCRIPTION AND MAP OF ITS PRINCIPAL PHYSICAL FEATURES BY THOMAS GWYN ELGER, F.R.A.S. DIRECTOR OF THE LUNAR SECTION OF THE BRITISH ASTRONOMICAL ASSOCIATION EX-PRESIDENT LIVERPOOL ASTRONOMICAL SOCIETY "Altri fiumi, altri laghi, altre campagne Sono la su che non son qui tra noi, Altri piani, altre valli, altre montagne." ORLANDO FURIOSO, Canto xxxii. LONDON GEORGE PHILIP & SON, 32 FLEET STREET, E.C. LIVERPOOL: 45 TO 51 SOUTH CASTLE STREET 1895 PREFACE This book and the accompanying map is chiefly intended for the use of lunar observers, but it is hoped it may be acceptable to many who, though they cannot strictly be thus described, take a general interest in astronomy. The increasing number of those who possess astronomical telescopes, and devote more or less of their leisure in following some particular line of research, is shown by the great success in recent years of societies, such as the British Astronomical Association with its several branches, the Astronomical Society of the Pacific, and similar institutions in various parts of the world. These societies are not only doing much in popularising the sublimest of the sciences, but are the means of developing and organising the capabilities of their members by discouraging aimless and desultory observations, and by pointing out how individual effort may be utilised and made of permanent value in almost every department of astronomy. The work of the astronomer, like that of the votary of almost every other science, is becoming every year more and more specialised; and among its manifold subdivisions, the study of the physical features of the moon is undoubtedly increasing in popularity and importance. To those who are pursuing such observations, it is believed that this book will be a useful companion to the telescope, and convenient for reference. Great care has been taken in the preparation of the map, which, so far as the positions of the various objects represented are concerned, is based on the last edition of Beer and Madler's chart, and on the more recent and much larger and elaborate map of Schmidt; while as regards the shape and details of most of the formations, the author's drawings and a large number of photographs have been utilised. Even on so small a scale as eighteen inches to the moon's diameter, more detail might have been inserted, but this, at the expense of distinctness, would have detracted from the value of the map for handy reference in the usually dim light of the observatory, without adding to its utility in other ways. Every named formation is prominently shown; and most other features of interest, including the principal rill-systems, are represented, though, as regards these, no attempt is made to indicate all their manifold details and ramifications, which, to do effectually, would in very many instances require a map on a much larger scale than any that has yet appeared. The insertion of meridian lines and parallels of latitude at every ten degrees, and the substitution of names for reference numbers, will add to the usefulness of the map. With respect to the text, a large proportion of the objects in the Catalogue and in the Appendix have been observed and drawn by the author many times during the last thirty years, and described in _The Observatory_ and other publications. He has had, besides, the advantage of consulting excellent sketches by Mr W.H. MAW, F.R.A.S., Dr. SHELDON, F.R.A.S., Mr. A. MEE, F.R.A.S., Mr. G.P. HALLOWES, F.R.A.S., Dr. SMART, F.R.A.S., Mr. T. GORDON, F.R.A.S., Mr. G.T. DAVIS, Herr BRENNER, Herr KRIEGER, Mr. H. CORDER, and other members of the British Astronomical Association. Through the courtesy of Professor HOLDEN, Director of the Lick Observatory, and M. PRINZ, of the Royal Observatory of Brussels, many beautiful photographs and direct photographic enlargements have been available, as have also the exquisite heliogravures received by the author from Dr. L. WEINEK, Director of the Imperial Observatory of Prague, and the admirable examples of the photographic work of MM. PAUL and PROSPER HENRY of the Paris Observatory, which are occasionally published in _Knowledge_. The numerous representations of lunar objects which have appeared from time to time in that storehouse of astronomical information, _The English Mechanic_, and the invaluable notes in "Celestial Objects for Common Telescopes," and in various periodicals, by the late REV. PREBENDARY WEBB, to whom Selenography and Astronomy generally owe so much, have also been consulted. As a rule, all the more prominent and important features are described, though very frequently interesting details are referred to which, from their minuteness, could not be shown in the map. The measurements (given in round numbers) are derived in most instances from NEISON'S (Nevill) "Moon," though occasionally those in the introduction to Schmidt's chart are adopted. THOMAS GYWN ELGER. BEDFORD, 1895. CONTENTS INTRODUCTION MARIA, OR PLAINS, TERMED "SEAS" RIDGES RING-MOUNTAINS, CRATERS, &C. Walled Plains Mountain Rings Ring-Plains Craters Crater Cones Craterlets, Crater Pits MOUNTAIN RANGES, ISOLATED MOUNTAINS, &c. CLEFTS, OR RILLS FAULTS VALLEYS BRIGHT RAY-SYSTEMS THE MOON'S ALBEDO, SURFACE BRIGHTNESS, &c. TEMPERATURE OF THE MOON'S SURFACE LUNAR OBSERVATION PROGRESS OF SELENOGRAPHY, LUNAR PHOTOGRAPHY CATALOGUE OF LUNAR FORMATIONS FIRST QUADRANT West Longitude 90 deg. to 60 deg. West Longitude 60 deg. to 40 deg. West Longitude 40 deg. to 20 deg. West Longitude 20 deg. to 0 deg. SECOND QUADRANT East Longitude 0 deg. to 20 deg. East Longitude 20 deg. to 40 deg. East Longitude 40 deg. to 60 deg. East Longitude 60 deg. to 90 deg. THIRD QUADRANT East Longitude 0 deg. to 20 deg. East Longitude 20 deg. to 40 deg. East Longitude 40 deg. to 60 deg. East Longitude 60 deg. to 90 deg. FOURTH QUADRANT West Longitude 90 deg. to 60 deg. West Longitude 60 deg. to 40 deg. West Longitude 40 deg. to 20 deg. West Longitude 20 deg. to 0 deg. MAP OF THE MOON First Quadrant Second Quadrant Third Quadrant Fourth Quadrant APPENDIX Description of Map List of the Maria, or Grey Plains, termed "Seas," &c. List of some of the most Prominent Mountain Ranges, Promontories, Isolated Mountains, and Remarkable Hills List of the Principal Ray-Systems, Light-Surrounded Craters, and Light Spots Position of the Lunar Terminator Lunar Elements Alphabetical List of Formations INTRODUCTION We know, both by tradition and published records, that from the earliest times the faint grey and light spots which diversify the face of our satellite excited the wonder and stimulated the curiosity of mankind, giving rise to suppositions more or less crude and erroneous as to their actual nature and significance. It is true that Anaxagoras, five centuries before our era, and probably other philosophers preceding him, certainly Plutarch at a much later date taught that these delicate markings and differences of tint, obvious to every one with normal vision, point to the existence of hills and valleys on her surface; the latter maintaining that the irregularities of outline presented by the "terminator," or line of demarcation between the illumined and unillumined portion of her spherical superficies, are due to mountains and their shadows; but more than fifteen centuries elapsed before the truth of this sagacious conjecture was unquestionably demonstrated. Selenography, as a branch of observational astronomy, dates from the spring of 1609, when Galileo directed his "optic tube" to the moon, and in the following year, in the _Sidereus Nuncius_, or "the Intelligencer of the Stars," gave to an astonished and incredulous world an account of the unsuspected marvels it revealed. In this remarkable little book we have the first attempt to represent the telescopic aspect of the moon's visible surface in the five rude woodcuts representing the curious features he perceived thereon, whose form and arrangement, he tells us, reminded him of the "ocelli" on the feathers of a peacock's tail, a quaint but not altogether inappropriate simile to describe the appearance of groups of the larger ring-mountains partially illuminated by the sun, when seen in a small telescope. The bright and dusky areas, so obvious to the unaided sight, were found by Galileo to be due to a very manifest difference in the character of the lunar surface, a large portion of the northern hemisphere, and no inconsiderable part of the south-eastern quadrant, being seen to consist of large grey monotonous tracts, often bordered by lofty mountains, while the remainder of the superficies was much more conspicuously brilliant, and, moreover, included by far the greater number of those curious ring- mountains and other extraordinary features whose remarkable aspect and peculiar arrangement first attracted his attention. Struck by the analogy which these contrasted regions present to the land and water surfaces of our globe, he suspected that the former are represented on the moon by the brighter and more rugged, and the latter by the smoother and more level areas; a view, however, which Kepler more distinctly formulated in the dictum, "Do maculas esse Maria, do lucidas esse terras." Besides making a rude lunar chart, he estimated the heights of some of the ring- mountains by measuring the distance from the terminator of their bright summit peaks, when they were either coming into or passing out of sunlight; and though his method was incapable of accuracy, and his results consequently untrustworthy, it served to demonstrate the immense [...]... to the northeastern quadrant, and including an area of about 340,000 square miles These are by far the largest lunar "seas." The Mare Foecunditatis, in the western hemisphere, the greater part of it lying in the southwestern quadrant, is scarcely half so big as the Mare Imbrium; while the Maria Serenitatis and Tranquilitatis, about equal in area (the former situated wholly north of the equator, and the. .. of the moon in which they do not abound, whether it be on the ramparts, floors, and outer slopes of walled and ring plains, the summits and escarpments of mountain ranges, amid the intricacies of the highlands, or on the grey surface of the Maria In many instances they have a brighter and newer aspect than the larger formations, often being the most brilliant points on their walls, when they are found... some of the ridges are as much as 700 feet in height, and probably in many instances the other elevations often rise to 150 feet or more above the low-lying parts of the plains on which they stand Hence we may say that the Maria are only level in the sense that many districts in the English Midland counties are level, and not that their surface is absolutely flat The same may be said as to their apparent... portions of the slope; but this fails to explain the symmetrical arrangement of the concentric terraces and intermediate valleys The inner declivity of the north-eastern wall of Plato exhibits what to all appearance is an undoubted landslip, as does also that of Hercules on the northern side, and numerous other cases might be adduced; but in all of them the appearance is very different from that of the. .. of philosophers, mathematicians, and other celebrities; and Cassini determined by actual measurement the relative position of many of the principal objects on the disc, thus laying the foundation of an accurate system of lunar topography; while the labours of T Mayer and Schroter in the last century, and of Lohrmann, Madler, Neison (Nevill), Schmidt, and other observers in the present, have been mainly... by a massive but much broken wall, which at one peak towers more than 9000 feet above a level floor, which includes details of a very remarkable character The adjoining _Alphonsus_ is another, but somewhat smaller, object of the same type, as are also _Albategnius_, and _Arzachel_; and _Plato_, in a high northern latitude, with its noble many-peaked rampart and its variable steel-grey interior _Grimaldi_,... near the eastern limb (perhaps the darkest area on the moon) , _Schickard_, nearly as big, on the southeastern limb, and _Bailly_, larger than either (still farther south in the same quadrant), although they approach some of the smaller "seas" in size, are placed in the same category The conspicuous central mountain, so frequently associated with other types of ringed enclosures, is by no means invariably... existence of the relics of an earlier lunar world beneath their smooth superficies MARIA. Leaving, however, these considerations for a more particular description of the Maria, it is clearly impossible, in referring to their level relatively to the higher and brighter land surface of the moon, to appeal to any hypsometrical standard All that is known in this respect is, that they are invariably lower than the. .. Ultimately, however, coming to the conclusion that terraces, as a rule, are not due to any such freaks of the eruption, he ascribes them to landslips In any case, we can hardly imagine that material standing at such a high angle of inclination as that forming the summit ridge of many of the ring-plains would not frequently slide down in great masses, and thus form irregular plateaus on the lower and flatter... is very generally of a dusky hue, similar to that of the grey plains or Maria, and, like them, is usually variegated by the presence of hills, ridges, and craters, and is sometimes traversed by delicate furrows, termed clefts or rills _Ptolemaeus_, in the third quadrant, and not far removed from the centre of the disc, may be taken as a typical example of the class Here we have a vast plain, 115 miles . represented are concerned, is based on the last edition of Beer and Madler's chart, and on the more recent and much larger and elaborate map of Schmidt; while as regards the shape and details of. THE MOON A FULL DESCRIPTION AND MAP OF ITS PRINCIPAL PHYSICAL FEATURES BY THOMAS GWYN ELGER, F.R .A. S. DIRECTOR OF THE LUNAR SECTION OF THE BRITISH ASTRONOMICAL ASSOCIATION. position of many of the principal objects on the disc, thus laying the foundation of an accurate system of lunar topography; while the labours of T. Mayer and Schroter in the last century, and of