Question 1609Navigation General

The correct answer is B) during twilight observations only. The phase correction is applied to sights of Venus and Mars when they are observed during twilight, either in the morning or evening. This is because the illuminated portion of the planet's disk changes as it orbits the Sun, and this needs to be accounted for to obtain an accurate celestial observation. The other options are incorrect because phase correction is not necessary at altitudes above 25° (option A), nor is it required during daytime observations (option D). Phase correction is specifically applied during twilight observations of Venus and Mars (option B).