Celestial Navigation · Sextant — Artificial Horizon
When a sextant altitude is taken using an artificial horizon (e.g., a reflecting pool ashore), the reading must be:
- ACorrected for semidiameter twice
- BDoubled, then dip subtracted
- CUsed directly with the normal dip correction
- DHalved to get the true altitude, with no dip correction applied✓ Correct
Explanation
An artificial horizon reflects the body, so the sextant measures the angle between the body and its reflection — twice the true altitude. The reading is halved to obtain the apparent altitude, and because the reference is the local horizontal rather than the sea horizon, no dip correction is applied.
Authority: Bowditch (Pub. No. 9), The Artificial Horizon
Practice the full Celestial Navigation bank
Free spaced-repetition quizzing across 2190 USCG exam questions — it schedules your reviews so the ones you miss come back until they stick.
Related Celestial Navigation questions
- Time
The Nautical Almanac tabulates the positions of celestial bodies against which time standard?
- Time
A vessel in west longitude has a zone description of +5. To convert zone time to UT you must:
- Coordinates
How is the GHA of a star obtained from the Nautical Almanac?
- Coordinates
Sidereal Hour Angle (SHA) is best defined as:
- Coordinates
Declination of a celestial body is the celestial equivalent of:
- The Nautical Almanac
Approximately how fast does the GHA of the Sun increase with time?