Which are the three vertices of the navigational triangle?

The correct answer identifies the three critical points that form the navigational triangle, which is essential in celestial navigation. This triangle involves the observer's position on Earth, the celestial body's position in the sky, and a reference point, typically described as the assumed position.

When navigating, the observer's geographic location is key to understanding where they are in relation to celestial objects. The position of a celestial body, indicated by its geographic coordinates, provides the necessary reference against which the observer's position is measured. The assumed position is a hypothetical or estimated location that navigators use to simplify calculations and establish a point from which to measure angles and distances to celestial bodies.

The other options, while they consist of significant geographical and astronomical points, do not represent the triangle's vertices used in navigational practice. For instance, mentioning the poles or the equator does not relate directly to the observer's process in celestial navigation. The equator, zenith, and prime meridian deal with different concepts in geography and mapping but do not encompass the specific triangulation needed for accurate navigation at sea. Thus, understanding the relationship between the observer, the celestial body, and the assumed position is foundational for effective navigational skills using celestial methods.