Nadir is employed during remote sensing of the atmosphere, as well as when an astronaut faces the Earth while performing a spacewalk. The term nadir can also be used to represent the lowest point reached by a celestial body during its apparent orbit around a given point of observation. This can be used to describe the location of the Sun, but it is only technically accurate for one latitude at a time and only possible at the low latitudes. The sun is said to be at the nadir at a location when it is at the zenith at the location's antipode
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