ASNSW Book Reviews

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“OBSERVING COMETS”

Author: Nick James and Gerald North
Reviewed by: Greg Bryant

It’s an exciting year for comets. Two long-awaited visitors, LINEAR and NEAT, were putting on a fine display in April at 4th magnitude, while one of the most fascinating aspects of comets – the unpredictability as to when new ones are discovered – was dramatically illustrated at Easter when South Australian amateur Bill Bradfield’s 18th comet discovery was announced. It reached magnitude -2 on SOHO images and was sighted in the Northern Hemisphere dawn sky at 4th magnitude as I was writing this.

In that light, it was an opportune time to read “Observing Comets”. At the outset, let me say that of the 20+ books in my library that are solely devoted to comets, this is the first that extensively addresses the topic of digitally photographing comets, but more on that later.

Visual observation of comets, the method which the majority of us would (still) use these days, is addressed in the first four chapters of the book. The anatomy, origin, and appearance of comets are well discussed. In fact, the book has one of the best collections of comet drawings I have seen in a popularly accessible book.

Don’t understand how comets are named these days? What does C/2001 Q4 really mean? It’s all well explained in the first chapter – though a recent change in policy, not noted in the book, is to only label newly discovered comets with orbits of less than 30 years as “periodic” (the previous upper limit on periods was 200 years). Those comets with orbits of greater than 30 years get to join the “periodic catalog” when they are seen to be returning, the most recent example being two years ago when comet C/2002 C1 (Ikeya-Zhang) was discovered, and soon afterwards it was identified as being the return of a bright comet seen in February and March of 1661 – accordingly Ikeya-Zhang received the prefix of 153P, the 153rd comet to be sighted at two or more returns.

The casual visual observer will be well served by what the authors cover, though I note that for those interested in trying to estimate a comet’s brightness, the sole method outlined in the book is not the approach used most commonly by the leading comet observers of today.

Observing is for many of us a “sightseeing” trip, and one tends to take cameras on daylight sight-seeing to record what is witnessed. The way that digital photography (in whatever camera format) has evolved and become so accessible in recent years, I believe that within the next 5 – 10 years, most of us will incorporate photography as part of our nightly observations. Just look at what was seen this year at SPSP, and the interest in the Digital Astroimaging Section of the club.

Accordingly, nearly half of the book deals with photographing techniques (digital primarily, but film is still mentioned) and associated computer activities – indeed, examples of these are included in the accompanying CD. The authors are very much in their element here, and it’s taken me one step closer to tackling digital imaging myself.

So… Where to here from here? Comet observing is an aspect of our hobby that possesses its own challenges. Rarely will you find a comet of even binocular brightness near the meridian at any time of night (they tend to be sights that favour the early evening and morning skies) and bright comets are few and far between. Still, if your interest in comets has been whetted by this year’s moderately bright comets, and you’re looking to observe the fainter variety (which I recommend that you do so that you can better appreciate the delight of the spectacular apparitions), this year has several telescopic comets worth following. Additionally, another comet, C/2003 T4 (LINEAR) has been discovered that could be seen in even small telescopes next Autumn, and May 2006 has the prospect of the returning comet 73P/Schwassmann- Wachmann being visible to the unaided eye.

And who knows what awaits discovery in the days and months ahead? Following comets is certainly not dull!

With that in mind, this book is well worth working through (either cover to cover, or picking the chapters that best suit your interest) to take to a new level your understanding of comets and how to observe them. It’s a valuable addition to the ASNSW library.