Celestial Theory Part 8a: How to determine your Local Hour Angle (LHA) in celestial Navigation
28 March 2025 · 13 min · 2K views · Malta
What this video covers
Celestial navigation requires selecting an assumed position (AP) that aligns with the pre-calculated data found in sight reduction tables. These tables provide the calculated altitude (Hc) and azimuth only for whole-degree increments of latitude and Local Hour Angle (LHA). To determine the correct AP, a navigator must first round their estimated position’s latitude to the nearest whole degree. Determining the LHA involves a more complex adjustment because the Greenwich Hour Angle (GHA) of the sun is fixed by the precise time of the observation, while the navigator’s own longitude is negotiable. By slightly shifting the assumed longitude, the navigator ensures the difference between their position and the sun’s GHA results in a whole-degree LHA. This adjustment allows the use of standard sight reduction tables to compare the calculated altitude against the observed altitude (Ho), with the resulting difference—the intercept—plotted as a line of position. While computer apps can calculate celestial fixes for any coordinate, manual navigation relies on these specific assumed positions to bridge the gap between estimated coordinates and tabular data.
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