During evening twilight on 28 December , the sextant altitude (hs) of the planet Venus was 29°43.2'. The height of eye was 40 feet, and the index error was 2.0' on the arc. What was the observed altitude (Ho)?

29°34.1' ✓ Correct Answer

29°36.0'

29°36.3'

29°38.2'

USCG NMC Regulatory Explanation

Index error occurs when the sextant index mirror and horizon glass are not parallel at 0° 00.0'. 'On the arc' errors are subtracted; 'off the arc' errors are added to sextant altitude readings.

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During evening twilight on 28 December , the sextant altitude (hs) of the planet Venus was 29&#176;43.2'. The height of eye was 40 feet, and the index error was 2.0' on the arc. What was the observed altitude (Ho)?

Question Discussion & Notes