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 join by crossing the upwind threshold and then turning downwind. With other traffic present in the circuit, the aircraft might be positioned downwind in the circuit behind or between other traffic in order to land in turn. Alternatives to the overhead join are to directly join the circuit by entering at a suitable corner, or a straight-in approach. If available, ATC will negotiate with the pilot which is the most appropriate method according to the current traffic situation. Standard Overhead Join 3-D diagram Standard Overhead Join poster reference Overhead join An overhead join is a conventional method for an aircraft to