na·dir /ˈneˌdɪr, ˈnedɚ/
 天底,最底點,最低點


 Na·dir 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.   --Hallam.
 Nadir of the sun Astron., the axis of the conical shadow projected by the earth.

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 nadir
      n 1: an extreme state of adversity; the lowest point of anything
           [syn: low-water mark]
      2: the point below the observer that is directly opposite the
         zenith on the imaginary sphere against which celestial
         bodies appear to be projected [ant: zenith]