The great circle of the celestial sphere that passes through the zenith, nadir, and the eastern point of the horizon is the __________.

Correct Answer: Option A — prime vertical

The prime vertical is the great circle passing through the zenith, nadir, and the east and west points of the horizon. It is a fundamental reference circle in the horizon system of coordinates, used to determine the azimuth of celestial bodies when they are rising or setting, per Bowditch.