Physics of the magnetosphere

Physics of the magnetosphere

BOOK REVIEWS a n d man:~ m o r e . I t m a y b e felt t h a t t h e p r o b l e m s in this section appeal more strongly to the author, w h o is a p r...

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BOOK REVIEWS a n d man:~ m o r e . I t m a y b e felt t h a t t h e p r o b l e m s in this section appeal more strongly to the author, w h o is a p r o m i n e n t a s t r o p h y s i c i s t , t h a n t h e m o r e prosaic exercises in a s t r o m e t r y . M a n y p r o b l e m s of m o d e r n a s t r o n o m y are p r e s e n t e d in t h e exercises; h o w e v e r , t h e r e is a t l e a s t one i m p o r t a n t t o p i c l a c k i n g - - a t m o s p h e r i c refraction, which, by the way, explains the often o b s e r v e d s t r o n g f l a t t e n i n g of t h e disks of t h e S u n a n d M o o n w h e n n e a r t h e horizon. T h e d e t e r m i n a t i o n of t h e t i m e of sunrise a n d s u n s e t for a g i v e n place c o u l d also b e d e a l t w i t h a n d p e r h a p s t h e m o r e c o m p l i c a t e d rising a n d s e t t i n g of t h e Moon. A few r e m a r k s m a y b e m a d e . T h e p o l a r d i s t a n c e of P o l a r i s a t p r e s e n t is 52' a n d n o t t h e 70' g i v e n o n p. 22, w h i c h p e r t a i n s t o a m o r e r e m o t e t i m e - - a b o u t 1910. I n t h i s c o m m c t i o n it should be noted that when giving the equatorial c o o r d i n a t e s of s t a r s e v e n w i t h s u c h a low precision as ± 1 ' or e v e n 0.1 o, t h e e p o c h of e q u i n o x s h o u l d a l w a y s b e s t a t e d . F i g u r e 31 on p. 69 is n o t d r a w n t o scale, as t h e d i a m e t e r o f t h e E a r t h ' s s h a d o w is a b o u t 2.5 t i m e s larger t h a n t h a t of t h e M o o n ' s d i s k a n d n o t 3.5 t i m e s as s h o w n i n t h e figure. T h e J u l i a n D a y s ( p r i n t e d w i t h a - before t h e l a s t t h r e e figures) are first u s e d o n p. 73, t h e e x p l a n a t i o n b e i n g g i v e n o n l y o n p. 195. Some of t h e exercises are v e r y i n g e n i o u s a n d will s t i m u l a t e t h e i n t e r e s t of t h e s t u d e n t s , e x a c t i n g t h e i r a b i l i t y t o a h i g h degree. As a s u m m a r y we c a n e m p h a s i z e t h e usefulness of t h i s book. A l t h o u g h it w o u l d b e difficult t o use i t in extenso, as n o t e v e r y o b s e r v a t o r y or e v e n u n i v e r s i t y w o u l d possess all n e c e s s a r y i n s t r u m e n t s a n d m a t e r i a l s , following t h e spirit of t h e exercises t h e y c a n b e a d a p t e d t o t h e m e a n s available. T h e b o o k is v e r y well p r o d u c e d a n d will b e a v a l u a b l e i m p l e m e n t for a n y i n s t i t u t i o n w h e r e t h e t e a c h i n g of a s t r o n o m y is p r a c t i c e d . A. MIKHAILOV

Pulkovo Observatory Leningrad M - 140 U.S.S.R. Physics of the Magnetosphere. E d i t e d b y R. L. CAROV~LLANO, J . F. McCLAY, a n d H . R . RADOSKI. S p r i n g e r - V e r l a g N e w Y o r k , 1968. 686 p p . P r i c e $39.00. I m u s t confess t h a t I b e g a n m y e x a m i n a t i o n of t h i s u n a b a s h e d l y e x p e n s i v e b o o k s o m e w h a t d u b i o u s l y . All t o o o f t e n c o n f e r e n c e p r o c e e d i n g s are little m o r e t h a n g u e s t rides o n s o m e n o t a b l e ' s f a v o r i t e h o b b y horse, o p a q u e t o t h e n o n e x p e r t , t e d i o u s t o t h e e x p e r t , a n d p r o b a b l y wrong, else so m u c h effort w o u l d n o t n e e d b e e x p e n d e d t o k e e p i t going. B y a n d large, Physics of the

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Magnetosphere is a p l e a s a n t l y s u r p r i s i n g dep a r t u r e f r o m t h a t n o r m . T h e b o o k is d i v i d e d i n t o t w o p a r t s : (I) t u t o r i a l l e c t u r e s b y h i g h l y r e g a r d e d e x p e r t s i n t h e i r r e s p e c t i v e fields--P a r k e r , Dessler, Helliwell, V a n Allen, a n d D u n g e y , a n d (II) i n v i t e d r e s e a r c h papers. T h e first p a r t is a l m o s t h a l f t h e book, w i t h 19 contributions rounding out Part II. The editors have transcribed the spoken p r e s e n t a t i o n s of t h e t u t o r i a l lectures, t o g e t h e r with graphic and written materials provided by t h e speakers, i n t o a r e m a r k a b l y clear a n d lucid p r e s e n t a t i o n . A n i m p r e s s i v e a m o u n t of t i m e a n d effort m u s t h a v e b e e n r e q u i r e d t o so effectively w r i t e u p s o m e o n e else's ideas, m a k e corrections, r e m o v e m i s c o n c e p t i o n s , satisfy t h e original a u t h o r , etc. I t a p p a r e n t l y was w o r t h t h e effort. U n l i k e p u b l i s h e d papers, t h e s e lectures h a v e h a d t o b e clear t o a t least one o t h e r i m p a r t i a l s c i e n t i s t (i.e., one of t h e editors). As a r e s u l t t h e y will b e f o u n d t o b e clear to m a n y . (The t r a d i t i o n a l process o f r e f e r e n c i n g m a n u s c r i p t s for professional j o u r n a l s r a r e l y m a k e s m u c h i m p a c t o n style a n d p r e s e n t a t i o n . H e r e t h e referee h a s e s s e n t i a l l y written t h e m a n u s c r i p t . ) O f p a r t i c u l a r i n t e r e s t are t h e t r e a t m e n t s of h y d r o m a g n e t i s m (Parker), solar w i n d e x p a n s i o n (Dessler), t r a p p e d p a r t i c l e s ( V a n Allen), w h i s t l e r s (Helliwell), a n d i n s t a b i l i t i e s (Dungey). T h e editors have taken an unusually egalitarian a p p r o a c h i n allowing both M K S a n d e g s - g a u s s i a n u n i t s t o b e u s e d as t h e a u t h o r s ' desire. Since e a c h section is self-contained, t h a t p r o c e d u r e s e e m s t o cause n o difficulty. O n l y occasional errors are m a d e i n p r e s e n t i n g e q u a t i o n s - - o n e e x a m p l e is o n p. 152 ( V a n Allen) w h e r e t h e wellk n o w n e q u a t i o n s for t h e S t S r m e r f o r b i d d e n - z o n e loci h a v e b e e n hopelessly garbled. T h e c o n f u s i o n is c o m p o u n d e d o n p. 154, w h e r e i n t h e w r o n g l i m i t is t a k e n t o o b t a i n t h e e q u a t i o n for a dipole line of force. I h a v e n o t n o t i c e d o t h e r s u c h o b v i o u s errors. Questions, replies, a n d a n e c d o t e s h a v e b e e n g a t h e r e d a t t h e c o n c l u s i o n of e a c h of t h e five t u t o r i a l s a n d serve well t o p r o b e some of t h e less w i d e l y a c c e p t e d c o m m e n t s of t h e lecturers. P a r t I I is n e c e s s a r i l y a s o m e w h a t m i x e d bag, b u t m a n y i m p o r t a n t topics are discussed i n a d e t a i l n o t f o u n d elsewhere. O n l y a s m a l l m i n o r i t y are, for all i n t e n t s , s i m p l y r e p r i n t s . C o n t r o v e r s i a l m a t e r i a l (e.g., t h e d e t a i l e d s t r u c t u r e o f collisionless shocks) is o f t e n c o v e r e d f r o m o n l y one view, but at worst that view at least records the e x i s t i n g s t a t e o f knowledge. I w o u l d single o u t t h e p a p e r b y S p r e i t e r et al. o n t h e A e r o d y n a m i c s (s/c) of t h e M a g n e t o s p h e r e for p r o v i d i n g a p a r t i c u l a r l y d e t a i l e d discussion of t h e b o w s h o c k w a v e a n d h y d r o m a g n e t i e flow a r o u n d t h e

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BOOK REVIEWS

E a r t h ' s m a g n e t o p a u s e (such terms, ineidently, are explained b y P a r k e r on t h e v e r y first page of P a r t I). The d a t a presented in b o t h parts largely represent a c c u m u l a t e d observations from m a n y satellites. Out to a b o u t 6 E a r t h radii there is good accord, a n d future observations are m o r e likely to refine t h a n o v e r t h r o w these data. F a r from the E a r t h where one is in t h e u n p e r t u r b e d solar w i n d t h e d a t a are no less consistent b u t less well understood in fine detail. I n b e t w e e n (especially b e t w e e n 6 and 10 E a r t h radii, and in t h e tail of t h e magnetosphere) one still has a s o m e w h a t inconsistent or incomplete picture. Confidence in m a n y of the i n t e r p r e t a t i o n s presented should be weighted accordingly. F o r example, t h e r a t e of access of particles into t h e tail seems to v a r y widely a m o n g and e v e n w i t h i n the available observations. Such d a t a is directly r e l e v a n t to w h a t happens to the tail at large distances, which remains a controversial question. F o r t h e student, this book presents an exceedingly valuable introduction to t h e theory, observation, and literature of t h e m a g n e t o sphere. E v e n the researcher in one of t h e m a n y areas e m b r a c e d u n d e r t h e title will find t h a t the d e p t h and scope of t h e lecturers p r o v i d e valuable new insights. F. C. MICHEL

Space Science Department Rice University Houston, Texas 77001 Physics and Dynamics of Meteors. E d i t e d b y L. KRESAK and P. M. MILLikAN. I n t e r n a t i o n a l Astronomical Union, S y m p o s i u m No. 33, September 1967, T a t r a n s k a L o m n i c a , Czechoslovakia. Reidel Publ. Co., Dordreeht, H o l l a n d & Springer Verlag, N e w York, 1968. xiii + 525 pp. Price $27. This v o l u m e is t h e o u t c o m e of an i n t e r n a t i o n a l g a t h e r i n g in which scientists f r o m E a s t and W e s t joined in a t h o r o u g h discussion of t h e diverse p r o b l e m s of m e t e o r research. A m o n g t h e 66 participants, there were 19 from Czechoslovakia, 13 from t h e U S S R , 13 f r o m t h e U n i t e d States, 4 from England, 3 each from W e s t G e r m a n y a n d Canada, 2 each from Sweden, E a s t Germany, I t a l y , F r a n c e a n d Australia, a n d 1 from J a p a n . I n t r o d u c e d b y a p h o t o g r a p h of t h e assembly (containing 57 participants), t h e 50 papers of t h e v o l u m e w i t h stimulating discussions cut t h r o u g h all t h e current tasks of t h e m e t e o r researcher, from t h e d e t e r m i n a t i o n and statistics of orbits, t h e distribution of masses a n d velocities, to t h e

physics of m e t e o r flight in t h e atmosphere, being chiefly limited to t h e smaller c o m p o n e n t s of i n t e r p l a n e t a r y particulate m a t t e r below meteorite size from a mass of a b o u t 1 kg d o w n to zodiacal dust. T h e observational emphasis is n o w on r a d a r and precise photographic work, a l t h o u g h visual observations are still useful a n d are given their proper place, especially in t h e r e a l m of telescopic meteors, or in following up unusual shower displays such as t h e Leonids in N o v e m b e r 1966. I n this respect e v e n old Chinese records are p r o v i n g of great value, showing t h a t t h e Leonids h a v e always been there for as long as records h a v e been kept, while our m o s t popular stream, t h e Perseids, seems to h a v e t u r n e d into t h e E a r t h ' s p a t h as late as 830 A.D. (Astapovi5 and T e r e n t ' e v a , p. 308). The scope of t h e v o l u m e is so wide, its t h e m e s often challenging and i n v i t i n g critical comments, t h a t giving a fair account of all t h e proceedings would result in almost a n o t h e r volume. Only a few points selected at r a n d o m can be m e n t i o n e d here. R a d a r observations of meteors indicate a v a r i a t i o n of atmospheric density with the solar cycle at t h e 100-km level, t h e m a x i m u m density coinciding w i t h the solar m i n i m u m of sunspots (Lindblad, p. 50); this is similar but opposite in phase to the v a r i a t i o n of t h e u p p e r m o s t atmosphere as derived from satellite drag which shows m a x i m u m density during sunspot m a x i m u m . A more intense heating of t h e u p p e r a t m o s p h e r e during solar m a x i m u m obviously can a c c o u n t for t h e p h e n o m e n o n , increasing t h e scale height, decreasing t h e density (at equal load and pressure) at the b o t t o m of p e n e t r a t i o n of t h e heating short w a v e radiation, and lifting up t h e top w i t h increased d e n s i t y at exospheric level. Telescopic meteors seem to be c o m p a c t grains, n o t dustballs, as t h e y are reaching deeper into t h e a t m o s p h e r e (to ~81 km) t h a n the v e r y m u c h m o r e massive o r d i n a r y dustball meteors (Kohoutek, p. 143) which disintegrate into clusters of small grains at a higher a l t i t u d e (at an a e r o d y n a m i c pressure or drag of a b o u t 104 dyne/cm2). Statistics of 15 000 r a d a r orbits (belonging to v e r y small meteors, mass limit 10 -3 gm) reveal v e r y different orbital characteristics as c o m p a r e d to t h e Smithsonian Super S c h m i d t photographic meteors (mass limit 0.1 gm) (LebedineS, p. 241). While t h e larger masses h a v e low orbital inclinations and are m o s t l y in direct orbital motion, w i t h v e r y few retrograde ones, t h e orbital inclinations of t h e r a d a r meteors are m o r e or less r a n d o m , w i t h m a n y high values a r o u n d 90 ° and m a n y retrograde orbits (i = 90-180°). The orbits of t h e small particles