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Mapping the sky to the page.

The Amateur Astronomer's Introduction to the Celestial Sphere

William Millar (Cambridge University Press, 2006). 299 pages. ISBN-13 978-0-521-67123-1. $40, paperbound.

A GOOD JOURNEY often includes a map. This is as true when you're driving cross-country as it is when you're star-hopping from Spica to the Sombrero Galaxy. Unfortunately, a map is useful only if you know how to read it. This is particularly problematic in astronomy, where the maps change with the hour as our planet drives through the seasons. Understanding the celestial sphere is a first and necessary step in learning how to find your way around our sky. The Amateur Astronomer's Introduction to the Celestial Sphere can help you take this initial step, but it should not be your only guide for your trip.


Written in a conversational tone and rich in analogies, this book addresses the reader as an old friend, invoking straightforward, thorough, and often richly illustrated examples. Unfortunately, the friend-to-friend writing style occasionally decays into glib or incomplete statements. For instance, William Millar writes that if science is defined too strictly, then modern astronomy wouldn't be considered science, but he doesn't explain why. Later he offhandedly refers to Earth's shadow as an unnoticed detail of life. Such statements work when chatting around a telescope at a star party, but in a book they leave the reader a bit wanting.

Overall, Celestial Sphere consistently reminded me of the conversations I hear at star parties where old-timers are mentoring newbies. This is both good and bad. Millar carefully lays out all the concepts that are likely to baffle beginners, leveraging the experience of one who knows where people normally stumble. This is good. And just as a casual lesson often circles and loops, reaching the target without taking a particularly direct path, this book wanders from topic to topic. This is bad. Millar often introduces a subject, but states that its explanation won't come until pages or even chapters later. While it's impossible to explain everything in full detail in a nice sequential order, the text could have flowed much smoother with minor reorganization.

And yet I found the sporadic mistakes in the text and drawings more significant than the structural problems. They are most unforgivable in a book geared toward beginners. For instance, Millar works hard to carefully explain through illustrations how the Sun will move in relation to Regulus as seen from both the Northern and Southern Hemispheres. Unfortunately, while getting the east-west changes correct, he misplaces the Sun, causing it to appear south of Regulus from the northern perspective and north of Regulus from the southern perspective. While many sky-related matters reverse as one crosses the equator, the Sun doesn't change how it aligns with the stars along the compass points. This simple mistake, laid out across multiple diagrams, can leave the novice with deep conceptual confusion.


Discussions with more advanced math and physics are relegated to the back of the book, along with other useful tables and reference lists. I found the glossary satisfyingly substantial (despite wrongly using "centigrade" instead of "Celsius").

This book is the first in a five-book series. Future titles will focus on the history of astronomy, the solar system, deep space, and cosmology. Celestial Sphere is a bit rough around the edges, and it leaves me hoping that a second printing will include corrections and clarifications. As the inaugural volume in a series, I see promise, and I hope that Millar will carry the lessons learned in writing this book into future editions.

The Amateur Astronomer's Introduction to the Celestial Sphere presents all the ins and outs of the celestial sphere, but some of the pieces are a bit scrambled in the translation from the sky to the page.

PAMELA GAY teaches physics and astronomy at Southern Illinois University at Edwardsville, home of the Fighting Cougars.
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Title Annotation:The Amateur Astronomer's Introduction to the Celestial Sphere
Author:Gay, Pamela L.
Publication:Sky & Telescope
Article Type:Book review
Date:Apr 1, 2007
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