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late 14c. as a term in astronomy, from Old French declinacion (Modern French déclinaison), from Latin declinationem (nominative declinatio), noun of action from past participle stem of declinare (see decline). It took on various other senses 15c.-17c., most now obsolete.
declination dec·li·na·tion (děk'lə-nā'shən)
A bending, sloping, or other deviation from a normal vertical position.
A deviation of the vertical meridian of the eye to one or the other side due to rotation of the eyeball about its anteroposterior axis.
in astronomy, the angular distance of a body north or south of the celestial equator. Declination and right ascension, an east-west coordinate, together define the position of an object in the sky. North declination is considered positive and south, negative. Thus, +90 declination marks the north celestial pole, 0 the celestial equator, and -90 the south celestial pole. The usual symbol for declination is the lowercase Greek letter delta (delta).