In general terms, the zenith's the direction pointing directly "above" a particular location (perpendicular, orthogonal). The concept of "above"'s more specifically defined in astronomy, geophysics and related sciences (for example, meteorology) as the vertical direction opposite to the force of gravity at a given location. The opposite direction, for example the direction of the gravitational force's called the nadir. The term zenith's also used to represent the highest point reached by a cele… (More on Zenith)