Sight Reduction Techniques
Sight Reduction is the process of solving the Navigational Triangle
for an Assumed Position and the position of an observed Celestial Body
in order to obtain a Line-of-Position.
The basic underlying problem is solving the trigonometric relations
of a spherical triangle. Since this problem arises not only in earth-bound
navigation but in a variety of fields such as astronomy and geodesy, it
was a popular research topic for mathematicians for over centuries.
In the seventeenth century, John Napier (1550-1617) proposed a method of
solving the oblique navigational triangle by dividing it into two
right-angled triangles, which can be solved with less complex
Unlike the use of the spherical laws of cosines, Napiers Rules involve only
products and quotients of trigonometric functions, and are thus very practical
for logarithmic computation. Since also the principle of logarithms, was
first developed by John Napier, he provided a complete practical toolbox for
solving mathematical problems related to spherical triangles.
The following links provide a set of methods for performing the
Sight Reduction problem as it appears in Celestial Navigation.
Some methods, such as those proposed by Ageton and Bygrave are
still based on the previous achievements of John Napier.
Techniques for performing the Sight Reduction Process