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The Collaborative International Dictionary
Right descension

Descension \De*scen"sion\, n. [OF. descension, L. descensio. See Descent.] The act of going downward; descent; falling or sinking; declension; degradation.

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. [Obs.]