Question 1608Navigation General

The correct answer is C) the Sun's declination is zero. When the Sun's declination is zero, its center is coincident with both the celestial equator and the observer's prime vertical circle. This happens twice a year, at the vernal and autumnal equinoxes, when the Sun crosses the celestial equator. The other options are incorrect because they do not describe a situation where the Sun's center is coincident with both the celestial equator and the prime vertical. The June and December solstitial points are the locations where the Sun reaches its maximum northern and southern declinations, respectively, but do not represent the condition of zero declination. Upper transit refers to the Sun's passage across the observer's meridian, which does not necessarily align the Sun's center with the celestial equator and prime vertical.