Celestial Navigation · Sextant Corrections — Parallax
For which body is parallax (horizontal parallax) the largest and most significant correction?
- AThe sun
- BThe moon✓ Correct
- CPolaris
- DNavigational planets only
Explanation
Parallax arises because observations are made from Earth's surface, not its center. It is inversely related to distance, so the nearby moon has a large horizontal parallax (up to about 1°), addressed by a dedicated HP correction; for the sun it is small and for stars negligible.
Authority: Nautical Almanac, moon altitude corrections; Bowditch (Pub. No. 9), parallax
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