Celestial Navigation · Twilight
Star and planet sights are normally taken during twilight because:
- AStars are brightest at midnight
- BBoth the stars and the sea horizon are visible at the same time✓ Correct
- CRefraction is zero during twilight
- DThe sextant cannot be used in full daylight
Explanation
A sextant altitude needs a clear sea horizon. At twilight the brighter stars are visible while the horizon is still sharp, giving a brief window to take a round of star sights. In full darkness the horizon disappears.
Authority: Bowditch (Pub. No. 9)
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