NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Latitude + Longitude calculations
From: Henry Halboth
Date: 2005 Jul 24, 22:38 -0400
From: Henry Halboth
Date: 2005 Jul 24, 22:38 -0400
Again, have spent a couple of weeks at NC beaches and was able to indulge myself in a number of celestial observations for Lat + Long. By testing oneself in a known position, some idea of personal accuracy can be obtained, as well as a real feel for the reliance which may be placed on observations based on a sea horizon. For those who may be interested, the following are offered . In all, a Plath vernier sextant was employed. IC = 00'24" on the arc. HE = 20-Ft. ZD = +4 July 5, 2005: Latitude by meridian transit - Sun's LL LAN = 13-12-37 LMT + 4 = GMT 17-12-37 DEC = 22-43-42 N hs 77-53-10 + corr 00-11-00 = ho 78-04-10 LAT = 89-59-60 - 78-04-10 + 22-43-42 = 34-39-32 North July 6, 2005: Latitude by meridian transit - Sun's LL LAN = 13-12-47 LMT + 4 = GMT 13-13-47 DEC = 22-37-40 N hs 77-47-10 + corr 00-11-00 = ho 77-58-10 LAT = 89-59-60 - 77-58-10 + 22-37-40 = 34-39-30 North July 8, 2005: Latitude by meridian transit - Sun's LL LAN 13-13-07 LMT + 4 = GMT 17-13-07 DEC = 22-24-21 N hs 77-33-15 + corr 00-11-00 = ho 77-44-15 LAT = 89-59-60 - 77-44-15 + 22-24-21 = 34-40-06 North July 10, 2005: Longitude by time sight - Sun's LL, bearing about 111 drgrees, true LMT = 11-36-04 + 4 = GMT = 15-36-03 DEC = 22-10-03 N LAT = 34-40-06 N by previous meridian transit hs 63-22-20 + corr 00-10-48 = ho 63-33-08 LHA = 26-39-15 E, by time sight formula GHA = 50-21-42 W, by NA Long = 77-00-57 West July 10, 2005: Latitude by meridian transit - Sun's LL LAN = 13-13-24 LMT + 4 = GMT 17-13-24 DEC 22-09-32 N hs = 77-20-20 + corr 00-11-00 = ho 77-31-20 LAT = 89-59-60 - 77-31-20 + 22-09-31 = 34-38-11 North July 12, 2005: Latitude + Longitude @ LAN by equal altitudes + reduction to meridian 1. For the Longitude AM obs @ chro time = 17-00-12; Sun's LL = 76-42-00 PM obs @ chro time = 17-26-59; Sun's LL = 76-42-00 Mean chro time of obs = 17-13-35.5 = GMT of LAN GHA Sun @ 17-13-35.5 = 76-59-06 West = Longitude 2. For the Latitude hs Sun's LL @ 17-00-12 = 76-42-00 DEC = 21-53-12 N GMT of LAN by equal altitudes = 17-13-35.5 Time of obs before LAN = 17-13-35.5 - 17-00-12 = 00-13-24 Altitude corr to meridian - Bowditch Tabs 29 + 30 = + 00-19-36 hs 76-42-00 + 00-11-00 + 00-19-36 = ho 77-12-36 @ transit LAT = 89-59-60 - 77-12-36 + 21-53-12 = 34-40-36 N 3. Position @ 13-00-12 LMT = Lat 34-40-36 N + Long 76-59- 06 W Note: If one were to "analyze the analyzed analysis", and, if the assumed correct Longitude given below is absolutely correct, there is roughly a 4.5 sec discrepancy in this solution, indicating possibly some unaccounted for chronometer or sight timing error - perhaps a combination of both.. However, as subsequently stated, I cannot be absolutely sure of the charted Longitude, nor can I deny the possibility of a small error in timing. There are a number of ways to resolve this error, but they seem to be beyond the purpose of this posting. July 14, 2005: Latitude by meridian transit - Moon's UL LTT = 19-13-36 + 4 = GMT 23-13-36 DEC = 10-55-40 S hs = 44-06-20 + corr 00-19-24 = ho 44-25-44 LAT = 89-59-60 - 44-25-44 - 10-55-40 = 34-38-36 North I was in position 34-40.073 N + 77-00.097 W. I cannot vouch for the accuracy of this position, as the location is somewhat off the beaten path, and may not be well charted on the map program available to me. Unfortunately, I do not have a GPS to verify it. Regardless, it is my opinion that these results demonstrate the average accuracy + repeatability attainable by celestial navigation, under good to average conditions, utilizing the sea horizon. As previously reported, the horizon used, at the edge of the Gulf Stream, is plagued with a light haze which may have induced a bit of foreshortening, with resultant altitudes a somewhat greater than true. I am surprised at the apparent accuracy demonstrated in the equal altitude solutions shown. I did experiment with equal altitudes many years ago at sea, and it is my recollection that results were comparable. It might prove interesting and informative if some of our members who employ an artificial horizon would give equal altitudes a try and report accordingly. Their value may be being understated in available literature as well as on this List. Henry