Celestial Navigation · Coordinates — GHA and Longitude
The longitude of a body's geographical position is obtained from its GHA by:
- AUsing GHA directly if 0°–180° W; if GHA > 180°, the GP longitude is (360° − GHA) E✓ Correct
- BAdding the observer's latitude
- CSubtracting the declination
- DMultiplying GHA by 15
Explanation
GHA is measured westward from Greenwich, 0° to 360°. If GHA is 0°–180° it equals west longitude of the GP; if GHA exceeds 180°, the GP is in east longitude at (360° − GHA). This links the almanac's hour angle to a position on the chart.
Authority: Bowditch (Pub. No. 9), Celestial Coordinates
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