NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: When did "time sights" fade away?
From: Henry Halboth
Date: 2011 Jul 21, 19:23 -0700
From: Henry Halboth
Date: 2011 Jul 21, 19:23 -0700
Gary,
You are obviously correct. Originally, both the time sight and the intercept methods were worked from a DR position and any comparison of results must be based on the use of the same position. BTW, there is no reason that an AP cannot be used with the Time Sight. Also, some small differences will appear when using conventional logarithmic tables - of no significance, however, to practical navigation,
Regards,
Henry
From: Gary LaPook <glapook@pacbell.net>
To: NavList@fer3.com
Sent: Thursday, July 21, 2011 1:26 PM
Subject: [NavList] Re: When did "time sights" fade away?The St. Hilaire and the time sight/azimuth methods will produce the same LOP only if the chosen AP for the St. Hilaire computation produces the exact same azimuth which will not normally be the case. However, since it is accepted practice to use an AP withing 30 NM of the DR we accept the slight inaccuracy in the final LOP as it is accurate enough for celestial navigation. The difference also disappears into the inherent errors of the observation. I posted before a study of thousands of observations taken by many experienced navigators and the standard deviation came out to about 1.5' so about a third of observations have errors greater than this. Bowditch, 1938, says to allow a two NM error band on each side of the LOP so the slight differences between these two methods, and with the Sumner method, can be ignored for practical navigation.gl
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