Question 1416Navigation General

The correct answer is A) horizon system. The navigational triangle uses parts of two systems of coordinates - the celestial equator system and the horizon system. The celestial equator system is based on the position of celestial bodies relative to the celestial equator, while the horizon system is based on the position of celestial bodies relative to the observer's local horizon. The other answer choices are incorrect because the astronomical system and the terrestrial system are not the second system of coordinates used in the navigational triangle, and the ecliptic system is a different celestial coordinate system not directly involved in the navigational triangle.