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## A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Position-Finding

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Longitude Sight, South Pacific, 1864 - Revisited
From: Henry Halboth
Date: 2018 Jun 26, 21:33 -0400
To all,
I have been fiddling with the subject sight since it appeared on NavList and, as a matter of general interest, have decided to publish the results of my fiddling. The Time Sight provides a perfectly valid solution of the astronomical triangle as employed in celestial navigation and has the further potential advantage of providing a purely mathematical solution to position finding without the need of resorting to the plotting of lines of position, althouh it is also quite adaptable to this later procedure. To illustrate how it was employed in line of position navigation I have recalculated the sight utilizing the more modern cosine-haversine formula and have included an azimuth calculation to facilitate the plotting of a line of position through the position demonstrated by the assumed Latitude and the determined Longitude - the so called tangent method, as opposed to the chord method whereby two separate postions are calculated and the line connecting them considered the LOP. The tangent method was employed at least throughout WWII, and favored by the Steamboat Inspectors on License Examinations. I have also calculated the intercept, utlilizing the Marc St Hillaire method to show the close agreement in the LOPs determined as between the two (2) methods. As I have no idea as to the height of eye aboard the Morgan I hae simply employed the altitude correction originally utilized in the calculation provided by Frank.
For anyone interested in the determination of position without the need for plotting LOPs, I suggest looking into the use of the Time Sight in conjunction with 1) Latitude by Moon, Venus, or Star Meridian Transit with Longitude by Time Sight, 2) Use of the so called "back and fill" method, wherein a morning Time Sight is taken and not worked until a Noon Latitude is obtained and corrected for the distance run or difference in Latitude between the sight times and the AM sight, as obtained by use of the Traverse Table, then worked using the more correct Latitude, or 3) Simply employing the Longitude Factor, as obtained from Table 35, of Bowditch, which see for full instruction.

I do hope that I have not made too many typos in the attachments.

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