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Solar eclipses and the ionospheres
228
BOOK KEVIERS
question of interstellar colonization may be properly considered. At such time, there would no longer be any pressure to escape from our planet and our species might instead be drawn outward in pursuit of entirely positive goals. STEVEN SOTER Astronomy Department University of California Berkeley, California 94720
Solar Eclipses and the Ionosphere. Edited by MICHAEL ANASTASSIADES. Plenum Press, New York and London, 1970. xiv + 309 pp. Price $32.00. This book contains the proceedings of a NATO Advanced Studies Institute on Solar Eclipses and the Ionosphere, held in Lagonissi, Greece, May 26-June 4, 1969. The conference was organized to discuss research connected with the May 20, 1969 annular eclipse over North Africa and southern Europe, but daba from several ot’her eclipses, particularly the November 12, 1966 total eclipse over South America, were also considered. A solar eclipse can in principle provide a great deal of information about the ionosphere which is otherwise difficult to obtain. The electron density in the ionosphere is governed by the production, loss, and transport of ionization. If the production term, the solar radiation, is varied rapidly in a known way, much can be learned about the loss processes, particularly in regions where transport effects are not important. Similar effects occur at sunrise and sunset, of course, but the variation is much slower and more difficult to analyze, due to the gradual occultation by the atmosphere of different wavelengths at different altitudes and times. Ionospheric data from a number of eclipses in the past thirty years or so have been analyzed, but with mixed results. The basic problem is that the ionizing flux is not simply proportional to the unocculted fraction of the visible solar disk, as has often been assumed. In the lowest part of the ionosphere (D region) a substantial portion of the ionization is due to x-rays from active sunspots; at higher altitudes (E and Fl regions) softer x-rays from the corona contribute, and so the eclipse is never total; at the height of maximum electron density and above (F2 layer) transport effects are never negligible, and in fact the maximum electron density usually increases during an eclipse at temperate latitudes because
of rapid downward diffusion of overlying ionization. Many of these problems are now becoming understood, particularly as our knowledge of the solar flux variation over a wide range of wavelengths improves. The book consists of 19 papers plus concluding remarks by two of the participant’s. The first three papers, by Bowhill, Rishbeth, and Thomas are fairly general reviews which summarize quite well the aspects of ionospheric physics relevant to eclipse observations and, particularly in Bowhill’spaper, the important results obtained in a number of eclipse measurements. The fourth paper, by Mitra, reviews in considerable detail the chemistry of the D region. Friedman provides an extensive review of the whole subject of solar ionizing radiation, and Krimigis and Wende deal in even greater detail with the subject of x-ray emissions. The remaining papers present data on onc or both of the 1966 eclipses, together with appropriate discussion which frequently includes comparison with the results of earlier eclipses. The D region was studied with rocket, partial reflection, and absorption measurements ; higher altitudes were observed with ionosondes (both ground based and topside) ; and effects on the total content were observed with Farada) rotation measurements which revealed a surprising increase in total content during the May 1966 eclipse. Unfortunately the interesting incoherent scatter measurements of electron density and temperature made in Peru during the November 1966 total eclipse were not presented at the conference, but similar measurements made by Evans in 1963 were discussed in Bowhill’s review. The electron temperature in the F region decreases very rapidly during an eclipse urltil it approaches equilibrium with the neutral gas. Data on microwave (h = 3.2, 6.0, 9.1, 11.1, and 21.lcm) and millimeter wave (h = l-30mm) radiation from the Sun during an eclipse were presented by Straka and Croom, respectively. What emerges from this book is a reasonably comprehensive and up to date picture of what happens in the ionosphere during an eclipse. Except, perhaps for the D region, thr important physical processes involved are understood. In order to achieve good quantit,ative agreement, between theory and experiment, however, we still require better knowledge of the solar eclipse functions appropriate to the different, altitude regions. As Bow-hill notes in his concluding summary of the conference, there is a great neecl for close collaboration among workers measuring different parameters using a variety of techniques. This conference represent,s a good start in that direction, and the proceedings should be
BOOK REVIEWS of value to those working in the field of ionospheric physics. DONALD T. FARLEY School of Electrical Engineering and Center for Radiophysics and Space Research Cornell University Ithaca, New York 14850
Principles of Celestial Mechanics. FITZPATRICK. Academic Press, New 1971.405pp. $12.75.
P. M. York,
In his acknowledgments, the author cites his son for the drawings, but makes no mention of critical review of the draft manuscript by any of his colleagues. The result of this failure of discipline is evident throughout the first half of the book. Danby’s Fundamentals of Celestial Mechanics (Macmillan, 1962) is still the best modern introductory text on the subject, at least in English. Hopefully, the latter author will not be offended by my saying that this is a great pity, for it is a reflection on his contemporaries, not him. Several books covering this material have appeared in recent years, but, most of the authors have fallen into one of two categories : (1) Industrial scientists unfamiliar with the requirements of textbook material, producing pedagogically unsound books ; or (2) theoreticians so “pure” that their horizons are so narrow that practical aspects are omitted, distorted, or badly handled. Fitzpatrick is in this latter group; Principles of Celestial Mechanics reads as though two different people wrote the two halves, divided neatly into Chapter l-6 and 9-14, with 7 and 8 serving as a transition. The overall effect of the first half has the unhappy burden of diluting one’s appreciation of the last sections of the book, which are in fact quite good. Since the book is not homogeneous, I will arbitrarily divide this review into Parts I and II for my own and the reader’s convenience. Part I (Chapters l-6). The numerous errors of fact mar the author’s credibility, but do not constitute a subtle hazard to the reader. Very little outside reading is required for most of them to be glaringly obvious. For example, the angular momentum vector is parallel, not perpendicular, to r x + (p. 40); acceleration of coordinate frames is important in satellite motions (p. 106); planetary precession is not 47” per year (p. 107); Venus’ “large” inclination is not the important cause of perturbations in Earth’s latitude (p. 107) ; Nutation in longitude has 17” amplitude, not 9” (p. 108); expression
229
for obliquity is wrong (p. 108). Most of these are inexcusable, but fairly transparent. Similar transparency would have been a great advantage in some other parts of the text. Seldom has the derivation of two-body motion been presented in such an obscure and complicated manner as here. To increase the “as seen through a glass, darkly” effect, much attention is given to a theological exercise in which the two-body problem is reduced to an “equivalent” one-body problem, in which the attractive force issues from an unaccelerated (but empty) point in inertial space. While we may not understand the nature of gravitation, we know a physical absurdity when one appears. Other topics that are obscured by theological distinctions or unphysical treatment are those involving reference frames that are unaccelerated but not “fixed” in inertial space, and the treatment of precession. The entire application of vectorial dynamics was handled more concisely and with greater clarity by Brand (Vectorial Mechanics, Wiley, 1930), as well as many writers since. In fact, Fitzpatrick gives clear evidence that his use of vector algebra is a grudging concession to the current trend, rather than arising from any understanding of the potential utility of this approach. Units and constants are troublesome. Once upon a time, the necessity of performing arithmetic operations in fixed-point mode gave rise to the idea of adopting units in which certain constants became identically unit,y (i.e. “canonic” units) and/or certain variables are of order unity (i.e. normalized units). The former device simplifies the equations, while the latter minimized the loss of relative accuracy. Both devices are introduced by Fitzpatrick, and I claim that both are a disservice to the student, because the justification is gone. Virtually no computing is done in fixed-point mode now, and any set of units is as good as any other from the machine’s point of view. From the programmer’s point of view, the best set of units is any, so long as it is always the same set for all objects. The only remaining “advantage” is the disappearance of parameters from the equations. But this is not bought cheaply, for the numerical results have to be the same, no matter the form of the equations, and the canonic form is conducive of computing errors. The canonic form is now only a means by which the theoretician transfers his burdens to the shoulders of the practitioner. In the development of canonic units, several physical parameters are given values which are used in the unit definitions. Among them are the Sun-Earth mass ratio, the astronomical unit, and Eart,h
BOOK KEVIERS
question of interstellar colonization may be properly considered. At such time, there would no longer be any pressure to escape from our planet and our species might instead be drawn outward in pursuit of entirely positive goals. STEVEN SOTER Astronomy Department University of California Berkeley, California 94720
Solar Eclipses and the Ionosphere. Edited by MICHAEL ANASTASSIADES. Plenum Press, New York and London, 1970. xiv + 309 pp. Price $32.00. This book contains the proceedings of a NATO Advanced Studies Institute on Solar Eclipses and the Ionosphere, held in Lagonissi, Greece, May 26-June 4, 1969. The conference was organized to discuss research connected with the May 20, 1969 annular eclipse over North Africa and southern Europe, but daba from several ot’her eclipses, particularly the November 12, 1966 total eclipse over South America, were also considered. A solar eclipse can in principle provide a great deal of information about the ionosphere which is otherwise difficult to obtain. The electron density in the ionosphere is governed by the production, loss, and transport of ionization. If the production term, the solar radiation, is varied rapidly in a known way, much can be learned about the loss processes, particularly in regions where transport effects are not important. Similar effects occur at sunrise and sunset, of course, but the variation is much slower and more difficult to analyze, due to the gradual occultation by the atmosphere of different wavelengths at different altitudes and times. Ionospheric data from a number of eclipses in the past thirty years or so have been analyzed, but with mixed results. The basic problem is that the ionizing flux is not simply proportional to the unocculted fraction of the visible solar disk, as has often been assumed. In the lowest part of the ionosphere (D region) a substantial portion of the ionization is due to x-rays from active sunspots; at higher altitudes (E and Fl regions) softer x-rays from the corona contribute, and so the eclipse is never total; at the height of maximum electron density and above (F2 layer) transport effects are never negligible, and in fact the maximum electron density usually increases during an eclipse at temperate latitudes because
of rapid downward diffusion of overlying ionization. Many of these problems are now becoming understood, particularly as our knowledge of the solar flux variation over a wide range of wavelengths improves. The book consists of 19 papers plus concluding remarks by two of the participant’s. The first three papers, by Bowhill, Rishbeth, and Thomas are fairly general reviews which summarize quite well the aspects of ionospheric physics relevant to eclipse observations and, particularly in Bowhill’spaper, the important results obtained in a number of eclipse measurements. The fourth paper, by Mitra, reviews in considerable detail the chemistry of the D region. Friedman provides an extensive review of the whole subject of solar ionizing radiation, and Krimigis and Wende deal in even greater detail with the subject of x-ray emissions. The remaining papers present data on onc or both of the 1966 eclipses, together with appropriate discussion which frequently includes comparison with the results of earlier eclipses. The D region was studied with rocket, partial reflection, and absorption measurements ; higher altitudes were observed with ionosondes (both ground based and topside) ; and effects on the total content were observed with Farada) rotation measurements which revealed a surprising increase in total content during the May 1966 eclipse. Unfortunately the interesting incoherent scatter measurements of electron density and temperature made in Peru during the November 1966 total eclipse were not presented at the conference, but similar measurements made by Evans in 1963 were discussed in Bowhill’s review. The electron temperature in the F region decreases very rapidly during an eclipse urltil it approaches equilibrium with the neutral gas. Data on microwave (h = 3.2, 6.0, 9.1, 11.1, and 21.lcm) and millimeter wave (h = l-30mm) radiation from the Sun during an eclipse were presented by Straka and Croom, respectively. What emerges from this book is a reasonably comprehensive and up to date picture of what happens in the ionosphere during an eclipse. Except, perhaps for the D region, thr important physical processes involved are understood. In order to achieve good quantit,ative agreement, between theory and experiment, however, we still require better knowledge of the solar eclipse functions appropriate to the different, altitude regions. As Bow-hill notes in his concluding summary of the conference, there is a great neecl for close collaboration among workers measuring different parameters using a variety of techniques. This conference represent,s a good start in that direction, and the proceedings should be
BOOK REVIEWS of value to those working in the field of ionospheric physics. DONALD T. FARLEY School of Electrical Engineering and Center for Radiophysics and Space Research Cornell University Ithaca, New York 14850
Principles of Celestial Mechanics. FITZPATRICK. Academic Press, New 1971.405pp. $12.75.
P. M. York,
In his acknowledgments, the author cites his son for the drawings, but makes no mention of critical review of the draft manuscript by any of his colleagues. The result of this failure of discipline is evident throughout the first half of the book. Danby’s Fundamentals of Celestial Mechanics (Macmillan, 1962) is still the best modern introductory text on the subject, at least in English. Hopefully, the latter author will not be offended by my saying that this is a great pity, for it is a reflection on his contemporaries, not him. Several books covering this material have appeared in recent years, but, most of the authors have fallen into one of two categories : (1) Industrial scientists unfamiliar with the requirements of textbook material, producing pedagogically unsound books ; or (2) theoreticians so “pure” that their horizons are so narrow that practical aspects are omitted, distorted, or badly handled. Fitzpatrick is in this latter group; Principles of Celestial Mechanics reads as though two different people wrote the two halves, divided neatly into Chapter l-6 and 9-14, with 7 and 8 serving as a transition. The overall effect of the first half has the unhappy burden of diluting one’s appreciation of the last sections of the book, which are in fact quite good. Since the book is not homogeneous, I will arbitrarily divide this review into Parts I and II for my own and the reader’s convenience. Part I (Chapters l-6). The numerous errors of fact mar the author’s credibility, but do not constitute a subtle hazard to the reader. Very little outside reading is required for most of them to be glaringly obvious. For example, the angular momentum vector is parallel, not perpendicular, to r x + (p. 40); acceleration of coordinate frames is important in satellite motions (p. 106); planetary precession is not 47” per year (p. 107); Venus’ “large” inclination is not the important cause of perturbations in Earth’s latitude (p. 107) ; Nutation in longitude has 17” amplitude, not 9” (p. 108); expression
229
for obliquity is wrong (p. 108). Most of these are inexcusable, but fairly transparent. Similar transparency would have been a great advantage in some other parts of the text. Seldom has the derivation of two-body motion been presented in such an obscure and complicated manner as here. To increase the “as seen through a glass, darkly” effect, much attention is given to a theological exercise in which the two-body problem is reduced to an “equivalent” one-body problem, in which the attractive force issues from an unaccelerated (but empty) point in inertial space. While we may not understand the nature of gravitation, we know a physical absurdity when one appears. Other topics that are obscured by theological distinctions or unphysical treatment are those involving reference frames that are unaccelerated but not “fixed” in inertial space, and the treatment of precession. The entire application of vectorial dynamics was handled more concisely and with greater clarity by Brand (Vectorial Mechanics, Wiley, 1930), as well as many writers since. In fact, Fitzpatrick gives clear evidence that his use of vector algebra is a grudging concession to the current trend, rather than arising from any understanding of the potential utility of this approach. Units and constants are troublesome. Once upon a time, the necessity of performing arithmetic operations in fixed-point mode gave rise to the idea of adopting units in which certain constants became identically unit,y (i.e. “canonic” units) and/or certain variables are of order unity (i.e. normalized units). The former device simplifies the equations, while the latter minimized the loss of relative accuracy. Both devices are introduced by Fitzpatrick, and I claim that both are a disservice to the student, because the justification is gone. Virtually no computing is done in fixed-point mode now, and any set of units is as good as any other from the machine’s point of view. From the programmer’s point of view, the best set of units is any, so long as it is always the same set for all objects. The only remaining “advantage” is the disappearance of parameters from the equations. But this is not bought cheaply, for the numerical results have to be the same, no matter the form of the equations, and the canonic form is conducive of computing errors. The canonic form is now only a means by which the theoretician transfers his burdens to the shoulders of the practitioner. In the development of canonic units, several physical parameters are given values which are used in the unit definitions. Among them are the Sun-Earth mass ratio, the astronomical unit, and Eart,h