A zenith is an imaginary point directly "above" a particular location, on the celestial sphere. It is the "highest" point on the celestial sphere. The word "zenith" derives from an inaccurate reading of the Arabic expression سمت الرأس (samt al-ras), meaning "direction of the head" or "path above the head", by Medieval Latin scribes in the Middle Ages (during the 14th century), possibly through Old Spanish. In a scientific context, the zenith is the direction of reference for measuring the zenith angle (or zenith angular distance), the angle between a direction of interest (e.g. a star) and the local zenith - that is, the complement of the altitude angle (or elevation angle). A zenith telescope is a type of telescope designed to point straight up at or near the zenith, and used for precision measurement of star positions, to simplify telescope construction, or for other purposes.