Nadir /(nā"dẽr)/

Na·dir

Nadir

n.
  1. That point of the heavens, or lower hemisphere, directly opposite the zenith; the inferior pole of the horizon; the point of the celestial sphere directly under the place where we stand.
  2. The lowest point; the time of greatest depression.
    The seventh century is the nadir of the human mind in Europe.

Phrases & Compounds
Nadir of the sun
the axis of the conical shadow projected by the earth.