83. Which term is given to the great circle of the celestial sphere that passes through the zenith, nadir, and the eastern point of the horizon?

The prime vertical is the great circle passing through the zenith, nadir, and eastern and western horizon points. This distinguishes it from the celestial meridian, which passes through the celestial poles, and hour circles, which are defined by right ascension rather than horizon points. Therefore, the correct answer is prime vertical.