©REESE PALLEY from CRUSING WORLD September 2010
Sun Sights: Easier Then The Sextant
for the device.
Ted Atherton, from the town of Wigan, England, ia a physicist dedicated to the process of simplification. He decided that traditional sextants are complicated, time-consuming, aggravating to use, and require the cooperation of sky and horizon. Resolved to build a better mousetrap, he spent a few hours at his kitchen table utilizing whatever materials came to hand and built an instrument he calls a heliostat, for which he's acquired a patent in England. As we stood aboard a square-rigged tea clipper off Tenerife, in the Canaries, he used his device to quickly determine the lat/long of our location
The heliostat requires no view of the horizon and only a quick glimpse of the sun to determine its elevation. It's especially useful when the sun is popping in and out of cloud cover. Anyone can be taught to use one in about a minute.
According to Ted, it's made from two semicircular sheets of plastic placed three millimeters apart. Each sheet has a blackened inner surface. One of the quadrants has an angular engraving that the sailor orients away from the sun when using the heliostat.
The elevation diagram shows how incoming sunlight enters the narrow space between the two blackened circular plates. A very narrow beam of sunlight encounters a small mirror in the center of the blackened base strip between the two plates. This small beam of sunlight, not absorbed by the blackened surfaces, is reflected by the mirror and exits the angularly calibrated section of the assembly, where it can be read without viewing the solar image directly. The heliostat is leveled by a pair of weighted gimbals or by a small, powered gyroscope.