Celestial Navigation · Sextant
The principal moving parts of a marine sextant used to measure an altitude are the index arm/mirror and the:
- AChronometer
- BAzimuth circle
- CHorizon glass (half-silvered)✓ Correct
- DPelorus
Explanation
The index mirror (on the movable index arm) reflects the body to the horizon glass, whose silvered half superimposes the body on the directly viewed horizon. The micrometer drum reads minutes of arc.
Authority: Bowditch (Pub. No. 9), the marine sextant
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