Doğru Cevap: zenith, nadir and the east point of the horizon

Açıklama: "Prime vertical is the great circle on the celestial sphere that passes through the zenith, nadir and the east point of the horizon" because it is the circle that passes through the point directly above the observer (zenith), the point directly below the observer (nadir), and the point on the horizon where the sun rises in the east.