John Karl provides the cleanest and most elegant introduction to the fundamental concepts of celestial navigation that I have read. I would even recommend this book to those who have a curiosity about how it all works but never intend to actually practice this ancient art.

He begins with a few essential fundamentals — a spherical earth with a surface organized via lines of longitude and latitude, celestial objects with known positions relative to a rotating earth, and an observer with a means to measure the apparent altitude of these celestial objects. These equal-altitude lines of position would really be circles if  “drawn” on a globe.

John then develops the concept of the “navigation triangle” and introduces the Nautical Almanac, which will provide some of the key parameters of the navigation triangle. Next, it’s on to the math required to do a direct computation solution using a handheld calculator. And finally, he shows how the results can be plotted as lines of position on a chart of appropriate scale. John does compare and contrast direct computation versus sight reductions with tables (H.O. 229 and H.O. 249).

John includes a chapter on ‘Special Sights’ with topics such as Polaris; meridian sights, including determining both latitude and longitude from meridian sights; finding time from a lunar line of position and a star fix. Then, John calmly takes the student to the holy grail of historical celestial navigation — lunar distances.

Only then, after he has helped his students put aside their angst about sight reductions, does John introduce the sextant and teach its use. The final chapter includes over 70 examples “for understanding and confidence.” Each includes useful comments to aid the learning process.

I recommend this book, without hesitation, to anyone with an interest in celestial navigation.

Celestial Navigation in the GPS Age by John Karl (Paradise Cay Publications, 2007; 280 pages)