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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Timed Noon sights for position
From: Doug Royer
Date: 2004 Jan 22, 15:25 -0800
From: Doug Royer
Date: 2004 Jan 22, 15:25 -0800
Bill,I don't understand what you're try to convey.If you took the noon sight while the DR was 30 m to the east the resulting GHA of the Sun would reflect that.The 120414zt time is only valid for the one EP.30 miles farther to the east(118*13'43"W)the time of local m.p. will be before 120414zt. I'm calculating the zone time(local)of local apperrant noon(local meridian passage)and the EP position of the vessel at that time.If the noon sight is taken when the Sun is centered on the local meridian the resulting altitude(when reduced)will give an estimation of the latitude.Because the Sun at this time is 180* north or south of the DR or EP the resulting * ' " of the GHA of the Sun will approximate the ships' longitude.One has to then open the N.A. and retrieve the whole degree,minutes and secounds of the GHA of the Sun for the time the sight was taken to approximate the longitude.Thus obtaining both estimates for lat and lon. As Joel stated taking double altitudes and Fred stated comparing ZT and GMT will also show the longitude at a noon sight. Timeing the shot is very important in this method.I was 12 sec. late on the 1-15-04 noon sight and the resulting position shows this error.The noon sight on 1-16-04 was 1 sec. late as to the calculated zt time of m.p.,along with a slower travel speed,and the resulting approximation of longitude was much closer to the gps position. Does this clear up what I was trying to get across? -----Original Message----- From: Navigation Mailing List [mailto:NAVIGATION-L@LISTSERV.WEBKAHUNA.COM]On Behalf Of Fred Hebard Sent: Thursday, January 22, 2004 14:12 To: NAVIGATION-L@LISTSERV.WEBKAHUNA.COM Subject: Re: Timed Noon sights for position Yes, it overcomes most objections, although the procedure is fairly inaccurate, up to about 100 miles, compared to time shots a few hours before and maybe after noon. But Doug is saying that's better than nothing. Also, Doug appears to be using a different procedure in his detailed posting. On Jan 22, 2004, at 4:58 PM, Joel Jacobs wrote: > Let me suggest, that if Doug had the time, he could start taking > sights, say > 5 minutes before Meridian Passage, record his first reading, and if he > wants > a series of readings, until Meridian Passage, record that, and then > preset > his sextant to the first altitude he observed, and take the time when > the > sun reached that altitude on the downside after passage. Averaging > those two > times should allow him to solve for long. > > That's more time than he wanted to allocate to this, but it shouldn't > it > overcome the objections relative to getting long from a noon sight. > > Joel Jacobs > >