The correct answer is A) meridian angle. In the navigational triangle, the angle at the elevated pole represents the meridian angle, which is the angle between the meridian and the vertical circle passing through the celestial body. This angle is used in various navigational calculations, such as determining the latitude and longitude of a vessel. The other options are incorrect because: B) Azimuth angle is the angle between the north-south line and the vertical circle passing through the celestial body. C) Altitude is the angle between the horizon and the celestial body. D) Right ascension is the celestial equivalent of longitude, measured eastward along the celestial equator.