Descension /(?)/

De·scen·sion

Descension

n.
  1. The act of going downward; descent; falling or sinking; declension; degradation.

Phrases & Compounds
Oblique descension
the degree or arc of the equator which descends, with a celestial object, below the horizon of an oblique sphere.
Right descension
the degree or arc of the equator which descends below the horizon of a right sphere at the same time with the object.