books book reviews

solar astrophysics books

reviewed by T. Nelson


Solar Astronomy Handbook
by Rainer Beck, Heinz Hilbrecht, Klaus Reinsch, & Peter Völker

T his 516-page book was originally published in Germany as Handbuch für Sonnenbeobachter in 1982. The focus is on observational techniques in visible light that are affordable by amateur astronomers. It's an excellent way for the non-scientist to become familiar with solar astronomy. Most of the imaging and computer technology described here (film cameras, mainframe computers, etc.) are only of historical interest, but the basic facts about the Sun haven't changed.

The authors give advice on topics where our understanding is incomplete and the amateur could contribute. The amateur can't compete with professional physicists who have institutional support. For example, magnetic fields (which are analyzed by measuring the Zeeman effect) and ultraviolet measurements are impractical for most individuals. But amateurs can make descriptive observations that can contribute to knowledge in other ways. The key to getting good data is understanding the limitations of the method. To this end the authors provide extensive discussions of the problems with measuring faculae and working with Wolf numbers, which are still used in measuring sunspot indexes.

There is a chapter on Hα, but little on other wavelengths except for a brief list in the chapter on the corona, and nothing about non-optical phenomena like neutrinos. There is little on photometry or temperature estimation, which are important for pros. But there's an excellent chapter on photographing solar eclipses.

The authors use heliographic coordinates where West=Right, East=Left, and North=Up. Yes, astroboffins have somehow made this insanely simple topic confusing. Astronomers use “east” to mean the side that is on the east side of the Earth when looking up at the object when it's above the horizon and the west side of the Earth when it's below the horizon. If you were on the Sun, that would be your west. But the IAU (the same group that keeps changing its mind about whether Pluto is really a planet) changed it in 1961, so now only the Sun and some of the planets still use this direction. (I won't even mention Venus, which is upside-down and therefore opposite.) Just to be complete, this book sometimes uses one scheme, and sometimes the other. Is this confusing? Good! Confusion is the beginning of understanding. Or is it the other way around?

Whichever way it is, the authors suggest that amateurs can help by providing continuous ground observations that no professional can match. With today's technology, they can also produce images far surpassing those in this book. This book will get you oriented to the terminology if not to the geography, but you will need to know much more to obtain meaningful measurements.

An appendix contains an extensive bibliography of scientific and popular articles, many of which are in English.

nov 01 2014


Astrophysics of the Sun
by Harold Zirin

I f you really want to learn about the Sun, you can't do better than Harold Zirin's Astrophysics of the Sun. Solar astrophysicists see the universe from the other side of the globe—the sunny side, as it were, instead of the dark side. They see things differently.

If there's a drawback to this book, it's that Zirin gets so enthusiastic he forgets that he's not talking to other scientists. He spends several pages talking about Moreton waves, for instance, but forgets to say what the heck a Moreton wave is until fifty pages later. He also uses lots of shorthand slang that his fellow scientists will understand, but students won't. Example: what is a “continuum kernel?” It's part of the anatomy of a solar flare, but if he defined it somewhere I missed it.

This enthusiasm is probably why Zirin's students, by all accounts, loved him. He was enormously modest, evidenced in the Preface where he wrote “I have tried to understand everything I was writing about.” He also had a quirky sense of humor. For example, on page 100, after calculating the flux of neutrinos at the Earth, he says, “it is astonishing to contemplate such a huge flux passing through our bodies, no matter where we hide, and no doubt environmentalists will soon express concern over it.”

The first 5 chapters are the mandatory slogging through atomic spectroscopy and magnetohydrodynamics. But then, starting in Chapter 6, just when he starts talking about the Sun, things go a little wonky. Table 6.1, showing the relative abundance of the elements in the Sun, is off by a factor of 10x. He also uses incorrect notation for isotopes, putting mass number where everyone else puts charge. For example, one fusion reaction looks like this:
          2He3 + 2He44Be7 + γ.
This looks weird, and it's bound to confuse students. (The average layperson might not get this; but to a physicist it's as if someone wrote the formula for carbon dioxide as 2CO.)

Okay, so Zirin didn't care much about nuclear chemistry. His real passion was the chromosphere, sunspots, solar flares, and especially the corona. The writing here is lively, informative, and above all, modest, despite the fact that his work contributed greatly to our knowledge.

In the 26 years since this book was published, the mystery of sunspots that Zirin talks about has been largely solved, dedicated satellites have replaced many of our ground-based telescopes, and the X-ray images of the Sun in this book now look quaint. Fourteen million degrees is not enough to make the Sun a hot topic in astrophysics, and indeed for astronomers on the dark side it mostly just gets in the way. Despite its age, this book still may be the best way to learn about the Sun without getting a tan.

nov 08 2014