Celestial Navigation · Twilight
Star and planet sights are normally taken during nautical twilight because:
- AThe stars are brightest at midnight
- BRefraction is zero then
- CBoth the brighter stars and the sea horizon are visible at the same time✓ Correct
- DThe Sun's declination is greatest
Explanation
During morning/evening nautical twilight the horizon is still distinct while navigational stars are visible, allowing simultaneous altitude measurements. The almanac tabulates the times of twilight.
Authority: Bowditch (Pub. No. 9), twilight observations; The Nautical Almanac twilight tables
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