Celestial Navigation · Fix Quality — Star Selection Geometry
For the best three-star fix, the stars should be chosen so their azimuths are:
- ASpread roughly 120° apart around the horizon✓ Correct
- BAll within 30° of one another
- CAll near the observer's meridian
- DAll at altitudes above 70°
Explanation
Stars about 120° apart in azimuth (and at moderate altitudes of roughly 15°–65°) give lines of position that cross at strong angles, producing a small, well-conditioned fix triangle. Bodies bunched in azimuth give a weak fix, and very high or very low altitudes are harder to observe accurately.
Authority: Bowditch (Pub. No. 9), Selecting Stars
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