To get an intersect and thus a 

 fix, the entire procedure is done 

 again with a different celestial body. 



"The more bodies observed, the 

 better you can fix your position," 

 Beuth says. 



WOULDN'T IT BE 

 FASTER IF ... ? 



r 



V^/elestial navigation s 

 concept of intersecting circles is 

 similar to that of a GPS. Imagine a 

 constellation of satellites orbiting the 

 Earth, constantly emitting radio 

 signals that contain precise timing 

 and orbital information, data that can 

 be processed by GPS receivers on the 

 land, at sea or in the air. A timing 

 signal is used to determine a position 

 on the surface of an imaginary sphere 

 surrounding the satellite. To fix a 

 position, the device takes a reading 

 from four satellites, yielding four 

 spheres. Their point of intersection is 

 the navigator's — actually the 

 device's — exact position. 



The entire process of acquiring 

 satellites and obtaining a positional 

 fix takes roughly two minutes with a 

 commercially available civilian GPS 

 unit. And a handheld device is about 

 the size of a walkie-talkie. Thus, the 

 GPS simplifies the navigator's task 

 and streamlines the physical tools to 

 one easily toted electronic gizmo. 



So why even bother using 

 celestial navigation except in 

 emergencies? 



Most navigators don't. 



Ernst Hayman, a sailor in 

 Beaufort, relies solely on GPS. He 

 carries three units so that he's 

 assured one is always working 

 properly. Even so, he keeps handy 

 the instructional books, charts, tables 

 and tools for celestial navigation as 

 the ultimate backup to his GPS 

 devices. 



The attraction GPS holds over 



celestial is twofold for Hayman: speed 

 and accuracy. 



As a novice at celestial, he figures 

 using the technique would take up to 

 an hour. More experienced celestial 

 navigators might perform the compu- 

 tations in only 15 minutes. That 

 doesn't sound like a long time until 

 it's compared to the couple of minutes 

 needed to operate a GPS. Also, the 

 satellites can fix a position to within 

 10 meters (about 33 feet) — while the 

 average accuracy for a celestial fix is 

 within 1 mile. 



And celestial navigation requires 

 that the boater perform tasks exactly, 

 even when exhausted. 



"When you're tired, a GPS reads 

 just the same. It doesn't get tired," 

 Hayman says. 



But, as with all electronic 

 devices, it can fail. That's why Capt. 

 Guy Grant, a navigator in Wilmington, 

 uses both a GPS and celestial 

 navigation. 



"The prudent mariner should not 

 rely solely on one means of naviga- 

 tion," Grant says. "If a satellite goes 

 AWOL, then you've got something to 

 fall back on." 



He doesn't use celestial naviga- 

 tion exclusively, but neither does he 

 let his celestial skills waste away. In 

 fact, he maintains all of his books, 

 tables and tools in top shape. And he's 

 amazed that the U.S. Navy recently 

 announced it would no longer teach 

 celestial navigation skills to its 

 midshipmen. 



Grant says it's best for navigators 

 to know all the levels of navigational 

 technology and be able to use them, 

 "even to the glass of water with a 

 wooden needle in it" (a primitive 

 compass). 



And he knows no one who uses 

 only celestial navigation when on the 

 water. 



"Even a diehard sailor is going to 

 have a GPS stuck in his seat back," he 

 says. "But I don't know that he'd 

 admit it." 



SILENT WONDER - 

 BUT NOT MUCH HELP 



N 



X i avigators start at a specific 

 point, and they want to end up at a 

 specific point. To accomplish this by 

 means of the stars, a navigator must go 

 through all the necessary motions and 

 use the right equipment. 



Instructions for lifeboat navigation 

 explain how to cope without one 

 necessary element at a time, for 

 example the sextant or a clock, but not 

 all of them, says Beuth, the community 

 college instructor. 



So the stars alone won't do it. 



Constellations can help you see 

 where you are, says Lee Shapiro, 

 director of the Morehead Planetarium 

 in Chapel Hill. 



But using them to navigate is 

 almost impossible because the heavens 

 shift, he says. The night sky a sailor 

 sees off the North Carolina coast in 

 October will be different from the night 

 sky he sees in January. 



With no gadgets at all, a navigator 

 can use the North Star only to approxi- 

 mate direction, but he would have to 

 guess his latitude. While this approach 

 may have been enough to set some 

 folks off to sea in past times, modern 

 sailors demand more precision. 



"What we accept today as tolerable 

 would have been very different in the 

 1 7th and 1 8th centuries," says Shapiro. 

 "It's the difference between aiming for 

 North America and for the Statue of 

 Liberty." 



So if Whitman were alive today, 

 sailing the Atlantic and using the stars 

 to get back home, he would not be able 

 to avoid the charts and figures, the 

 mathematics and tools of nautical 

 astronomy. He could, however, gaze up 

 in awe at the stars before grabbing his 

 sextant, parallel rulers and charts. 



If he opted for a GPS instead, he 

 could look up in silent wonder at the 

 satellites. □ 



COASTWATCH 17 



