航海測天解算表之程式開發

The Program Development of the Sight Reduction Tables for Marine Navigation

截距法是目前測天解算法的主要方法，在早期尚未發明計算器時，為了處理截距法的計算問題，一般使用航海測天解算表作為計算工具。然而，在縮減表冊及內插修正的製表目標下，該表有其限制與誤差；此外，當天體位於觀測者天頂時之特例，其表列方位為90°，容易造成初學者的混淆。本文首先探討航海測天解算表的製表公式及三種查表解算方式，並針對天體位於上、下中天時之特例，詳加說明，進而採用其製表公式開發出航海測天解算程式。此自行開發程式均透過例題確認無誤，且在特例時會顯示警告視窗，大幅改善了航海測天解算表的表達方式。

The intercept method is mainly adopted in the field of sight reduction. Before the calculator had not been developed, navigators usually used the sight reduction tables as a tool to solve the calculating problem of the intercept method. However； the sight reduction tables are proposed for the purpose of compressing tables and tabular interpolation such that they always lead to inaccuracy of the results or limitation of their further applications. Besides, when the special case that the celestial body is above the zenith is encountered, the degree of azimuth is 90 shown in tables and it usually confuses the beginner. In this article, we do not only discuss the formulae of sight reduction tables and solve problems by consulting tables, but also illustrate the judgment of azimuth when the celestial body is above the zenith. Finally, the formulae are adopted to develop a sight reduction program for marine navigation. This self-developed program is validated with several examples in artificial process. Further more, the error and warning message can automatically appear in the special case and the program greatly improves expressions of the sight reduction tables.