NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Problem in equal altitudes of the sun around local apparent no on
From: Mal Misuraca
Date: 1997 Mar 10, 01:50 EST
From: Mal Misuraca
Date: 1997 Mar 10, 01:50 EST
A problem in equal altitudes of the sun before and after local apparent noon, with consideration for error caused by movement of the boat. . . . A sailboat en route to Hawaii on August 3, 1995, in dead reckoning position 28 degrees 24 minutes North, 143 degrees 22 minutes West, making course 231 degrees true, speed 4.5 knots, makes the following sextant observations (GMT) of the lower limb of the sun on that day: 21:09:00 77degrees 08.5 minutes 21:19:09 78 degrees 12.8 minutes 21:25:04 78 degrees 33.4 minutes 21:26:56 78 degrees 47.8 minutes 21:30:30 78 degrees 58.1 minutes 21:35:14 79 degrees 06.6 minutes 21:39:00 79 degrees 08.8 minutes 21:39:05 79 degrees 08.8 minutes 21:39:10 79 degrees 08.8 minutes 21:42:56 79 degrees 06.6 minutes 21:47:40 78 degrees 58.9 minutes 21:51:10 78 degrees 47.8 minutes 21:53:10 78 degrees 33.4 minutes 21:59:05 78 degrees 12.8 minutes 21:09:05 77 degrees 08.5 minutes When the navigator realized at 21:39:10 that the sun had ceased to gain in altitude over the horizon and was hovering without apparent change in altitude, she began to reset her sextant to the exact altitudes seen before local noon and one by one recorded the time of the same altitudes after noon, as the sun descended. She knew that the time half way between each set of paired altitudes was by definition local apparent noon. This was a better way to fix the time of local noon than when the sun was hovering and she could not tell precisely when it hit her meridian (longitude) and thus made out local apparent noon. Three questions are posed. First, what was the most probable time of local apparent noon (within 5 seconds) the navigator found? Second, what was the boat's latitude and longitude fix for local apparent noon on August 3? Third, what was the error in minutes of longitude for this fix for the fact that the boat was moving during this series of sextant shots? Anyone wishing to post an answer to these questions, please do so by March 25. The author's calculation will be published shortly thereafter, and the closest navigator(s) to the author's answer will be disclosed. An explanation of the author's answer will be provided at length, so that all readers may examine anew this unique position-finding method, which requires only a nautical almanac and very simple calculations, with no spherical trig or sight reduction tables. Finally, the author will compare the accuracy of the equal altitudes method to typical sight reduction methods, to see how equal altitudes stacked up. Mal Misuraca "Celestial in a Day" San Francisco, California "Passage East," Sausalito KO6KR