Celestial Navigation · Lower Limb vs Upper Limb
If the navigator observes the Sun's upper limb instead of the lower limb, the main almanac correction must be adjusted by:
- AAdding the dip twice
- BSubtracting about twice the semidiameter (a separate upper-limb correction)✓ Correct
- CIgnoring refraction
- DAdding the parallax
Explanation
The standard Sun correction assumes the lower limb. For the upper limb an additional correction (roughly minus the full diameter, about 2 × SD) is applied, listed in the almanac's altitude correction tables.
Authority: The Nautical Almanac, Sun altitude correction (upper limb)
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