Descension

n.
  1. The act of going downward; descent; falling or sinking; declension; degradation.
    2. Oblique descension (Astron.),
    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.