Question 1686Navigation General

70% to pass

Where do you find the semidiameter correction to be used to correct sextant observations of the stars?

A A correction of -0.5' should be applied to all star sights.
B It is included in the altitude corrections inside the front cover of the Nautical Almanac.
C Table 25 in Bowditch contains the correction.
D No semidiameter correction is used.
AI Explanation

The correct answer is D) No semidiameter correction is used. The semidiameter correction is only used when observing the sun or moon with a sextant. For observations of stars, no semidiameter correction is applied. This is because stars are effectively point sources, so their semidiameter is negligible and does not need to be accounted for. The other options are incorrect - there is no standard -0.5' correction for star sights, the semidiameter is not included in the altitude corrections in the Nautical Almanac, and there is no table in Bowditch that contains a semidiameter correction for stars.

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Official Resources
USCG Navigation Rules (COLREGS) 33 CFR Navigation Rules USCG National Maritime Center
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