Sight Reduction There is a plethora of ways in which sights can be reduced:
My aim is to describe some of these methods. I will assume that the reader understands basic concepts such as lines of position (LOPs), interecepts, latitude and longitude, the celestial sphere and hour angles. I will add a method when I have successfully used it. |
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Cloudy Weather
Ageton
Classic Ageton |
Cloudy Weather Johnson
In about 1875 AC Johnson RN published a slim book On Finding The Latitude and Longitude In Cloudy Weather, Etc. earning the author the nickname Cloudy Weather Johnson. The book went through many editions. The 1905 edition was the twenty-eighth. |
HO 211 Ageton
For many years I had assumed that Short methods were so called because they were quicker and easier than long methods such as the cosine-haversine formula and Norie. Recently, when I tried HO 211 Ageton (first published in 1931), I discovered that Short refers to the size of the tables. Ageton is a slim volume (50 pages) vs Norie (600+ pages) but (in my opinion) the method is confusing. There is (again in my opinion) just as much work as cos-hav/Norie. |
Classic Ageton
In 2015 Greg Rudzinski, a member of the Navlist forum, produced a modified Ageton table in which the A and B values are framed by sin and cos values. Greg's table can be used to solve the spherical triangle by the classic sin formula, hence the name of the table.
In the Ageton table A = log cosecant and B = log secant (both multiplied by 100,000) so the modified table can be used to solve the classic spherical triangle
The Sight Reduction form needs to be tidied up. I note that Rule 2 is not visible. |
Last Updated: Tuesday 9th August 2016