Celestial Navigation · Sextant Corrections — Apparent Altitude
Sextant altitude (hs) is 40°00.0'. Index error is 2.0' ON the arc and the dip correction is 5.0'. What is the apparent altitude (ha)?
- A39°55.0'
- B40°07.0'
- C39°57.0'
- D39°53.0'✓ Correct
Explanation
Index error ON the arc is subtracted: 40°00.0' − 2.0' = 39°58.0'. Then dip is subtracted: 39°58.0' − 5.0' = 39°53.0'. Apparent altitude is the sextant altitude corrected for index error and dip, before the main (refraction/SD/parallax) correction.
Authority: Nautical Almanac; Bowditch (Pub. No. 9), Sextant Altitude Corrections
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