The word zenith derives from an inaccurate reading of the Arabic expression سمت الرأس (samt al-raʾs), 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.[2] It was reduced to samt ("direction") and miswritten as senit/cenit, the m being misread as ni. Through the Old Frenchcenith, zenith first appeared in the 17th century.[3]
Angles and planes of a celestial sphereThe shadows of trees are the shortest on Earth when the Sun is directly overhead (at the zenith). This happens only at solar noon on certain days in the tropics, where the trees' latitude and the Sun's declination are equal.
The term zenith sometimes means the highest point, way, or level reached by a celestial body on its daily apparent path around a given point of observation.[4] This sense of the word is often used to describe the position of the Sun ("The sun reached its zenith..."), but to an astronomer, the Sun does not have its own zenith and is at the zenith only if it is directly overhead.
In a scientific context, the zenith is the direction of reference for measuring the zenith angle (orzenith 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 (orelevation angle).
At a given location during the course of a day, the Sun reaches not only its zenith but also its nadir, at the antipode of that location 12 hours from solar noon.
Inastronomy, the altitude in the horizontal coordinate system and the zenith angle are complementary angles, with the horizon perpendicular to the zenith. The astronomical meridian is also determined by the zenith, and is defined as a circle on the celestial sphere that passes through the zenith, nadir, and the celestial poles.
Azenith 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 both. The NASA Orbital Debris Observatory and the Large Zenith Telescope are both zenith telescopes, since the use of liquid mirrors meant these telescopes could only point straight up.
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 stars (also "star on top", "overhead star", "latitude star")[7] are stars which culminate (pass) through the zenith. Used in celestial navigation it allowed the navigator to determine their latitudal position, since at every latitude different stars pass one's zenith, or with other words lie on the great circle of the zenith ("zenith circle"). Zenith stars are not to be confused with "steering stars"[7] of a sidereal compass rose of a sidereal compass.
^Corominas, J. (1987). Breve diccionario etimológico de la lengua castellana (in Spanish) (3rd ed.). Madrid. p. 144. ISBN978-8-42492-364-8.{{cite book}}: CS1 maint: location missing publisher (link)
Media related to Zenith (topography) at Wikimedia Commons
Mathematics
Astronomy
Stars
Spaceflight
Outer space
Solar System
Science
