Celestial Navigation · Altitude Corrections — Nonstandard Conditions
When is the additional altitude correction for temperature and barometric pressure applied?
- AFor low-altitude sights in conditions far from the standard 10°C / 1010 mb, when refraction departs from the tabulated value✓ Correct
- BFor every sight regardless of altitude
- COnly for moon sights
- DOnly above 45° altitude
Explanation
The standard altitude correction assumes 10°C and 1010 mb. In cold/hot air or abnormal pressure the actual refraction differs, so the almanac's temperature/pressure additional correction is applied — most significant at low altitudes where refraction is large.
Authority: Nautical Almanac, additional corrections; Bowditch (Pub. No. 9)
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