Zenith On the International Space Station, "zenith" and "nadir" are used instead of "up" and "down", referring to directions within and around the station, relative to the earth. Zenith The zenith is an imaginary point directly "above" a particular location, on the imaginary celestial sphere. "Above" means in the vertical direction opposite to the apparent gravitational force at that location. The opposite direction, i.e. the direction in which gravity pulls, is toward the nadir. The zenith is the "highest" point on the celestial sphere. The word "zenith" derives from an inaccurate reading of the Arabic expression (), meaning "direction of the
Overhead line Overhead line An overhead line or overhead wire is used to transmit electrical energy to trams, trolleybuses or trains. It is known variously as: In this article, the generic term "overhead line" is used, as used by the International Union of Railways. An overhead line is designed on the principle of one or more overhead wires (or rails, particularly in tunnels) situated over rail tracks, raised to a high electrical potential by connection to feeder stations at regular intervals. The feeder stations are usually fed from a high-voltage electrical grid. Electric trains that collect their current from overhead lines use