The Noon Fix
The simplest possible backup to GPS. The only battery required is in the watch.
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When I first tried the double altitude method to determine longitude, I quickly found that north-south boat movement affected the time of maximum altitude. I immediately started looking for a simple, direct method of compensating for it. When none was forthcoming, I wrestled with the mathematics to derive the equation for the time between maximum altitude and meridian transit (in Position from Observation of a Single Body published in Navigation). That was a bit messy, but it worked. But recently, the simple, direct method hit me. Like many others, I slapped my head, muttering, “Why didn’t I think of this before?”
The approach is intended as a backup for GPS, and is for navigators who are familiar with the process of sight taking and reduction. Accordingly, only differences from that are described in detail.
While the method was aimed at getting the simplest backup to GPS, other uses may materialize. That it has the capability for more accuracy than the equation in Position from Observation of a Single Body published in Navigation (and its predecessor in the Admiralty Navigation Manual some fifty plus years earlier) could be of benefit.
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About the Book
A simple yet accurate method for determining position from observations of the Sun near noon is presented. It uses an enhancement of the graphical method presented in Position from Observation of a Single Body published in Navigation. An example is given, and a supply of sight reduction forms and graphs for plotting is included.
About the Author
James N. Wilson has taught celestial navigation since 1973, and has served on the Power Squadron Offshore Navigation Committee. He has also been a navigator on Pacific yacht races. His 1985 paper, Position from Observation of a Single Body was published in Navigation. A graduate of UC Berkeley and MIT, his professional career was at Caltech’s Jet Propulsion Laboratory. There he actively participated in the creation of the Mariner spacecrafts, which were the first to Venus, Mars and Mercury.