Nadir Nadir The nadir (, ; from / ALA-LC: "naẓīr", meaning "counterpart") is the direction pointing directly "below" a particular location; that is, it is one of two vertical directions at a specified location, orthogonal to a horizontal flat surface there. Since the concept of "being below" is itself somewhat vague, scientists define the nadir in more rigorous terms. Specifically, in astronomy, geophysics and related sciences (e.g., meteorology), the nadir at a given point is the local vertical direction pointing in the direction of the force of gravity at that location. The direction opposite the nadir is the zenith. Nadir is
Opposite group it is equal to its opposite group. Also, every group formula_1 (not necessarily abelian) is naturally isomorphic to its opposite group: An isomorphism formula_10 is given by formula_11. More generally, any antiautomorphism formula_12 gives rise to a corresponding isomorphism formula_13 via formula_14, since Let formula_16 be an object in some category, and formula_17 be a right action. Then formula_18 is a left action defined by formula_19, or formula_20. Opposite group In group theory, a branch of mathematics, an opposite group is a way to construct a group from another group that allows one to define right action as a special