Question 1694Navigation General

The correct answer is A) for inaccuracies in the instrument. When correcting the sextant altitude to apparent altitude, you are correcting for inaccuracies in the sextant instrument, such as index error. The sextant measures the angle between the celestial body and the visible horizon, but this angle (the "observed altitude") needs to be corrected to account for factors like the height of the observer's eye above the sea, atmospheric refraction, and other small errors. Applying these corrections gives the "apparent altitude" which is the true angle between the body and the celestial horizon. The other answer choices are incorrect because they do not accurately describe what is being corrected for when going from observed altitude to apparent altitude.