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Astronomical observations—an optical perspective
ICARUS 7 4 , 3 7 4 - 3 7 5
(1988)
BOOK REVIEWS Meteorite Craters. By Kathleen Mark. The University of Arizona Press, Tucson. 1987. 288 pp. $29.95. Science suffers from fashion too, and today meteorite craters are in fashion. But it was not always so. Back in 1665 Robert Hooke was writing about his attempts at producing a laboratory analog of the formation mechanism of lunar craters. First he dropped round bullets into a viscous mixture of clay and water and noticed that the resulting craters were similar to those seen on the Moon. But the formation of lunar craters by impacting objects was ruled out because "it would be difficult to imagine whence these bodies should come." Hooke returned to another experiment in which he heated dry gypsum powder in a pot. This released vapor that rose in bubbles, leaving behind replicas of lunar craters. His conclusion was that the craters were volcanic, and we had to wait for G. K. Gilbert (1893) to propound the first scientific lunar impact theory. Today with disappearing dinosaurs, airborn surveys of the Canadian shield, tektites, and the Barringer Crater in Arizona, impact craters are all the rage. This remarkable change of opinion has occurred since the beginning of the twentieth century. Today more than one hundred meteorite craters have been recognized and we can clearly see the results of the intense extraterrestrial bombardment that we have suffered. Kathleen Mark won the 1975 Nininger Award for her work on meteorite craters and in this book has presented us with a clear, comprehensive, and nontechnical history of their recognition. She writes well and obviously understands the slow and somewhat devious journey that accompanies the development and acceptance of a new scientific finding. Only from about 1960 has the collaboration of geologists, geophysicists, and astronomers led to the production of a clear set of recognition criteria. The nontechnical nature of the book makes it very easy to read, but does not hide the fact that the author has put in an enormous amount of hard work. Every idea, figure, and photograph is clearly referenced, making this book a superb springboard for anyone entering this fascinating field of research. Mark stresses the fact that the main problem was caused by the lack of appreciation of the amount of energy released. In the early 1930s F. R. Moulton and, independently, L. J. Spencer were the first to consider what happened when a meteorite of mass 100 tons hit the Earth at a speed of 40 kilometers per second. It penetrates the surface and in a very small fraction of a second is converted into an explosive "compared with which dynamite and T.N.T. are mild and
harmless . . . . The subjacent materials are forcibly compressed, whilst those above and around are shattered and pulverized and hurled aloft. In a few seconds a vast structure is fashioned which may preserve for untold geological ages the record of its birth." (to quote A. C. Gifford). To begin with, the craters are clearly circular, this being independent of the meteorite entry angle. Rock layers can be exposed which, less than 5 kilometers away, can be found 500 meters below the surface of the ground. For a second or so some of the rock would be subjected to pressures of between 35,000 and 130,000 atmospheres and temperatures between 700 and 1500°C, these pressures and temperatures being much greater than any that occur in volcanic events. Even diamond formation takes place in the meteorite. The effect of these conditions on the rocks led, in places, to the formation of deformed quartz lamellae, coesite, suevite, maskelynite, and shatter-cones. All these processes had to be tested under laboratory conditions before the disbelief drifted away. Kathleen Mark's account reveals the excitement of the subject. Imagine taking high-altitude photographs of parts of Ontario and then discovering the Brent Crater on them. Imagine standing on the rim of the Arizona Meteorite Crater in full view of a host of volcanic peaks, craterlets, and diatremes and finding coesite. Imagine wandering around the Vredefort Ring and through the Bushveld Igneous Complex and slowly realizing that a meteorite had played a part. To quote E. M. Shoemaker, it is now clear that "the impact of solid bodies is the most fundamental of all the processes that have taken place on the terrestrial planets . . . . Collision of smaller objects is the process by which the terrestrial planets were born." We must thank Kathleen Mark for making this subject so accessible to the general reader. DAVID W. HUGHES
University of Sheffield England
Astronomical Observations--An Optical Perspective. By Gordon Walker. Cambridge University Press, Cambridge, 1987. 400 pp., $79.50 hardcover. Gordon Walker has written a valuable book. Astronomical Observations--An Optical Perspective is an overview of modern astronomical instrumentation and techniques. While the emphasis is on optical astron374
0019-1035/88 $3.00 Copyright © 1988 by Academic Press, Inc. All rights of reproduction in any form reserved.
BOOK REVIEWS omy, the equipment and methods appropriate to other spectral regions are treated as well. The book is divided into eight chapters: astronomical sources; observational limits; telescopes; seeing, speckles, and scintillation; spectrographs; dilute apertures; single-channelled detectors; and multichannelled incoherent detectors. The first of these contains introductory discussions of the electromagnetic spectrum, thermal and nonthermal radiation, magnitudes and color indices, etc. The chapter on observational limits is concerned primarily with intrinsic constraints on the accuracy of astronomical observations. As one would expect, noise sources and detection limits are discussed, as are some of the difficulties caused by the atmosphere such as extinction. Oddly, this chapter also contains sections on celestial coordinates, precession, Julian Dates, aberration of starlight, astrometry, and radial velocity determination. These topics have little to do with observational limits; and, in some instances, their treatment here is so brief as to be misleading. The chapter on telescopes is excellent. Operating principles and design characteristics of ground-based and space-based telescopes operating in all regions of the spectrum from cosmic rays to radio wavelengths are described. Chapter 4 treats several topics of nearly universal interest to ground-based astronomers, including seeing, atmospheric turbulence, scintillation, and observatory site selection. The chapter also contains a clear discussion of speckle interferometry--a technique of rapidly growing importance in optical and infrared astronomy. A broad range of spectroscopic instrumentation is discussed in Chapter 5. Of particular interest to planetary scientists are sections dealing with echelle spectrographs, Fabry-Perot interferometers, and Fourier transform spectrometers since instruments of these types are often used for high-resolution studies of planetary atmospheres and comets. The chapter entitled "Dilute Apertures" is concerned with lunar occul-
375
rations and with interferometry in the optical and infrared and at radio wavelengths. Detectors, including photographic plates, photomultipliers, bolometers, radio receivers, image intensifiers, vidicons, CCDs, and many more, are covered in the final two chapters. I am sure that many readers will find these two chapters to be the most valuable part of the book. Illustrations, many of which are reproduced from other sources, are used liberally throughout this book, and the quality of the printing is excellent. Frequent references to the scientific literature are given, which will be helpful to individuals wishing to explore particular topics in greater detail. As with any new book, a few mistakes are present which should be corrected in later editions. These include a couple of serious grammatical errors (pages 11 and 196); a sign in Equation 1.15; text which is inconsistent with Figure 7.10, and a discussion of precession on page 54 that is misleading at best. These criticisms aside, the book does have much to offer. I was a bit surprised to read in the preface that the author intended this volume as a text for undergraduate students. Astronomical Observations struck me as more of an encyclopedia of observational astronomy. If you want a brief description of how X-ray detectors work, it is there. If you don't know what a MAMA is, this book will tell you. Do you need a clear definition of modulation transfer function, detective quantum efficiency, or noise equivalent power? You can find it quickly here. In short, Astronomical Observations is a handy reference book. I recommend it as such to advanced undergraduates, graduate students, practicing astronomers, and all others who need to understand the ever-expanding array of instrumentation and techniques being applied in astronomy today. ROBERT L. MILLIS
Lowell Observatory Flagstaff, Arizona
(1988)
BOOK REVIEWS Meteorite Craters. By Kathleen Mark. The University of Arizona Press, Tucson. 1987. 288 pp. $29.95. Science suffers from fashion too, and today meteorite craters are in fashion. But it was not always so. Back in 1665 Robert Hooke was writing about his attempts at producing a laboratory analog of the formation mechanism of lunar craters. First he dropped round bullets into a viscous mixture of clay and water and noticed that the resulting craters were similar to those seen on the Moon. But the formation of lunar craters by impacting objects was ruled out because "it would be difficult to imagine whence these bodies should come." Hooke returned to another experiment in which he heated dry gypsum powder in a pot. This released vapor that rose in bubbles, leaving behind replicas of lunar craters. His conclusion was that the craters were volcanic, and we had to wait for G. K. Gilbert (1893) to propound the first scientific lunar impact theory. Today with disappearing dinosaurs, airborn surveys of the Canadian shield, tektites, and the Barringer Crater in Arizona, impact craters are all the rage. This remarkable change of opinion has occurred since the beginning of the twentieth century. Today more than one hundred meteorite craters have been recognized and we can clearly see the results of the intense extraterrestrial bombardment that we have suffered. Kathleen Mark won the 1975 Nininger Award for her work on meteorite craters and in this book has presented us with a clear, comprehensive, and nontechnical history of their recognition. She writes well and obviously understands the slow and somewhat devious journey that accompanies the development and acceptance of a new scientific finding. Only from about 1960 has the collaboration of geologists, geophysicists, and astronomers led to the production of a clear set of recognition criteria. The nontechnical nature of the book makes it very easy to read, but does not hide the fact that the author has put in an enormous amount of hard work. Every idea, figure, and photograph is clearly referenced, making this book a superb springboard for anyone entering this fascinating field of research. Mark stresses the fact that the main problem was caused by the lack of appreciation of the amount of energy released. In the early 1930s F. R. Moulton and, independently, L. J. Spencer were the first to consider what happened when a meteorite of mass 100 tons hit the Earth at a speed of 40 kilometers per second. It penetrates the surface and in a very small fraction of a second is converted into an explosive "compared with which dynamite and T.N.T. are mild and
harmless . . . . The subjacent materials are forcibly compressed, whilst those above and around are shattered and pulverized and hurled aloft. In a few seconds a vast structure is fashioned which may preserve for untold geological ages the record of its birth." (to quote A. C. Gifford). To begin with, the craters are clearly circular, this being independent of the meteorite entry angle. Rock layers can be exposed which, less than 5 kilometers away, can be found 500 meters below the surface of the ground. For a second or so some of the rock would be subjected to pressures of between 35,000 and 130,000 atmospheres and temperatures between 700 and 1500°C, these pressures and temperatures being much greater than any that occur in volcanic events. Even diamond formation takes place in the meteorite. The effect of these conditions on the rocks led, in places, to the formation of deformed quartz lamellae, coesite, suevite, maskelynite, and shatter-cones. All these processes had to be tested under laboratory conditions before the disbelief drifted away. Kathleen Mark's account reveals the excitement of the subject. Imagine taking high-altitude photographs of parts of Ontario and then discovering the Brent Crater on them. Imagine standing on the rim of the Arizona Meteorite Crater in full view of a host of volcanic peaks, craterlets, and diatremes and finding coesite. Imagine wandering around the Vredefort Ring and through the Bushveld Igneous Complex and slowly realizing that a meteorite had played a part. To quote E. M. Shoemaker, it is now clear that "the impact of solid bodies is the most fundamental of all the processes that have taken place on the terrestrial planets . . . . Collision of smaller objects is the process by which the terrestrial planets were born." We must thank Kathleen Mark for making this subject so accessible to the general reader. DAVID W. HUGHES
University of Sheffield England
Astronomical Observations--An Optical Perspective. By Gordon Walker. Cambridge University Press, Cambridge, 1987. 400 pp., $79.50 hardcover. Gordon Walker has written a valuable book. Astronomical Observations--An Optical Perspective is an overview of modern astronomical instrumentation and techniques. While the emphasis is on optical astron374
0019-1035/88 $3.00 Copyright © 1988 by Academic Press, Inc. All rights of reproduction in any form reserved.
BOOK REVIEWS omy, the equipment and methods appropriate to other spectral regions are treated as well. The book is divided into eight chapters: astronomical sources; observational limits; telescopes; seeing, speckles, and scintillation; spectrographs; dilute apertures; single-channelled detectors; and multichannelled incoherent detectors. The first of these contains introductory discussions of the electromagnetic spectrum, thermal and nonthermal radiation, magnitudes and color indices, etc. The chapter on observational limits is concerned primarily with intrinsic constraints on the accuracy of astronomical observations. As one would expect, noise sources and detection limits are discussed, as are some of the difficulties caused by the atmosphere such as extinction. Oddly, this chapter also contains sections on celestial coordinates, precession, Julian Dates, aberration of starlight, astrometry, and radial velocity determination. These topics have little to do with observational limits; and, in some instances, their treatment here is so brief as to be misleading. The chapter on telescopes is excellent. Operating principles and design characteristics of ground-based and space-based telescopes operating in all regions of the spectrum from cosmic rays to radio wavelengths are described. Chapter 4 treats several topics of nearly universal interest to ground-based astronomers, including seeing, atmospheric turbulence, scintillation, and observatory site selection. The chapter also contains a clear discussion of speckle interferometry--a technique of rapidly growing importance in optical and infrared astronomy. A broad range of spectroscopic instrumentation is discussed in Chapter 5. Of particular interest to planetary scientists are sections dealing with echelle spectrographs, Fabry-Perot interferometers, and Fourier transform spectrometers since instruments of these types are often used for high-resolution studies of planetary atmospheres and comets. The chapter entitled "Dilute Apertures" is concerned with lunar occul-
375
rations and with interferometry in the optical and infrared and at radio wavelengths. Detectors, including photographic plates, photomultipliers, bolometers, radio receivers, image intensifiers, vidicons, CCDs, and many more, are covered in the final two chapters. I am sure that many readers will find these two chapters to be the most valuable part of the book. Illustrations, many of which are reproduced from other sources, are used liberally throughout this book, and the quality of the printing is excellent. Frequent references to the scientific literature are given, which will be helpful to individuals wishing to explore particular topics in greater detail. As with any new book, a few mistakes are present which should be corrected in later editions. These include a couple of serious grammatical errors (pages 11 and 196); a sign in Equation 1.15; text which is inconsistent with Figure 7.10, and a discussion of precession on page 54 that is misleading at best. These criticisms aside, the book does have much to offer. I was a bit surprised to read in the preface that the author intended this volume as a text for undergraduate students. Astronomical Observations struck me as more of an encyclopedia of observational astronomy. If you want a brief description of how X-ray detectors work, it is there. If you don't know what a MAMA is, this book will tell you. Do you need a clear definition of modulation transfer function, detective quantum efficiency, or noise equivalent power? You can find it quickly here. In short, Astronomical Observations is a handy reference book. I recommend it as such to advanced undergraduates, graduate students, practicing astronomers, and all others who need to understand the ever-expanding array of instrumentation and techniques being applied in astronomy today. ROBERT L. MILLIS
Lowell Observatory Flagstaff, Arizona