The correct answer is C) coaltitude. The navigational triangle is a spherical triangle formed by the celestial body, the zenith, and the elevated pole. The vertex of this triangle is not located at the coaltitude, which is the angular distance between the celestial body and the observer's horizon. Instead, the three vertices of the navigational triangle are the celestial body, the zenith, and the elevated pole. The other answer choices are incorrect because A) the celestial body is one of the vertices of the navigational triangle, B) the elevated pole is another vertex of the triangle, and D) the zenith is the third vertex of the triangle.