Under The Microscope

STARS AND THEIR SPECTRA: AN INTRODUCTION TO THE SPECTRAL SEQUENCE, By James B. Kaler; Cambridge University Press,1997; 300 pp; A$39.95

The Hertzsprung-Russell diagram is the Rosetta Stone of stellar astrophysics. First comes the abscissa: the ordering of the patterns of absorption and emission found in stellar spectra into a continuous, lettered classification immortalized by Harvard students' famous (or infamous) mnemonic: Oh! Be A Fine Girl, Kiss Me! The ordinate follows: the luminous output of the stars.

Kaler's book, first published in 1989 to excellent reviews and now reissued in paperback, is a tour across the Hertzsprung-Russell diagram, sweeping from the M stars, where the brightest are 50 billion times more luminous than the dimmest, to the O stars, where the range is a mere factor of ten. It is topped by introductory chapters on stellar names and properties, atomic spectroscopy and the history of spectral typing, and tailed by the Rosetta Stone deciphered: a masterful exposition of stellar evolution.

Kaler writes well, poetically even, and the copious illustrations are striking and apt, if somewhat classical. But, as earlier reviewers noted, the intended readership is unclear. Some discussion is very detailed, but mathematics is eschewed; the author finds it necessary to explain "mega" and "watt", but not "erg" and "gauss". This schizophrenia reflects the book's origin in a series of articles between 1986 and 1988 in Sky & Telescope, a magazine which is read by amateur and professional astronomers alike. It is nonetheless a splendid introduction to stellar botany for both audiences.

The text is announced "with corrections", and indeed a few discussions are slightly modified, such as planetary searches, supernovae and neutron-star mass limits. However, the book's 1980s origins are evident, with no mention that spectral typing has turned digital, while the claim that "no one fears the radio towers that fill space with low-energy electromagnetic radiation" astonishes in the loony 1990s. Spelling and editorial mistakes remain unrectified, as do factual errors signaled in earlier reviews. The reprinting is poor, with letters lacking crispness and occasional pages resembling poor photocopies, though the halftones are often better than in the 1989 edition.

These criticisms are nevertheless minor: Stars and their spectra has myriad virtues and taught me lots. I shall end this review as the book itself ends: "And tonight, if it is clear, go out and examine the real thing: all the classes arrayed for you, splashed wondrously across the darkened sky".

Dr William Tobin is in the Physics & Astronomy Department at Canterbury University.