Diagram showing the relationship between the Zenith, the Nadir, and different types of Horizon. Note that the Zenith is opposite the Nadir.

In broad terms, the zenith is the direction pointing directly above a particular location (perpendicular, orthogonal). Since the concept of being above is itself somewhat vague, scientists define the zenith in more rigorous terms. Specifically, in astronomy, geophysics and related sciences (e.g., meteorology), the zenith at a given point is the local vertical direction pointing away from direction of the force of gravity at that location. Look up zenith in Wiktionary, the free dictionary. ... Image File history File links Zenith-Nadir-Horizon. ... Image File history File links Zenith-Nadir-Horizon. ... For other uses, see Nadir (disambiguation). ... Horizon. ... Fig. ... In mathematics, orthogonal is synonymous with perpendicular when used as a simple adjective that is not part of any longer phrase with a standard definition. ... For other uses, see Astronomy (disambiguation). ... ‹ The template below has been proposed for deletion. ... // Meteorology (from Greek: μετέωρον, meteoron, high in the sky; and λόγος, logos, knowledge) is the interdisciplinary scientific study of the atmosphere that focuses on weather processes and forecasting. ... In astronomy, geography, geometry and related sciences and contexts, a direction passing by a given point is said to be vertical if it is locally aligned with the gradient of the gravity field, i. ... Gravity redirects here. ...

For reference, the vertical direction at the given location and pointing in the same sense as the gravitational force is called the nadir. For other uses, see Nadir (disambiguation). ...

Zenith is also used for the highest point reached by a celestial body during its apparent orbit around a given point of observation. [1] Often used in this sense about the Sun, it only corresponds to the first concept of zenith for one latitude at a time, and never at all for latitudes outside the tropics. Sol redirects here. ... This article is about the geographical term. ... A noontime scene from the Philippines on a day when the Sun is almost directly overhead. ...

Origin

The word zenith derives from the inaccurate reading of the Arabic word samt ('path'), pronounced sent, by scribes in the Middle Ages (during the 14th century), in the expression samt arrâs ('path above the head'). The Middle Ages formed the middle period in a traditional schematic division of European history into three ages: the classical civilization of Antiquity, the Middle Ages, and modern times, beginning with the Renaissance. ...

Relevance and use

The zenith is used in the following scientific contexts:

• It serves as the direction of reference for measuring the zenith angle, which is the angular distance between a direction of interest (e.g., a star) and the local zenith, relative to the point for which the zenith is defined.
• It defines one of the axes of the horizontal coordinate system in astronomy.

The horizontal coordinate system is a celestial coordinate system that uses the observers local horizon as the fundamental plane. ...

Discussion

• The zenith directions corresponding to three different locations (not on the same vertical direction) are divergent.
• Strictly speaking, the zenith is only approximatively contained in the local meridian plane because the latter is defined in terms of the rotational characteristics of the celestial body, not in terms of its gravitational field. The two coincide only for a perfectly rotationally symmetric body. On Earth, the axis of rotation is not fixed with respect to the planet (for example due to constant displacements of its fluid components) so that the local vertical direction, as defined by the gravity field, is itself changing direction in time (for instance due to lunar and solar tides).

Only between the tropics is it possible for the Sun to be at the zenith.

This article is about the astronomical concept. ... In astronomy, geography, geometry and related sciences and contexts, a direction passing by a given point is said to be vertical if it is locally aligned with the gradient of the gravity field, i. ... This article is about tides in the ocean. ... Image File history File linksMetadata Size of this preview: 800 × 548 pixels Full resolution (1280 × 876 pixel, file size: 1. ... Image File history File linksMetadata Size of this preview: 800 × 548 pixels Full resolution (1280 × 876 pixel, file size: 1. ... Sol redirects here. ...

See also

• Zenith distance
• Geodesy
• History of geodesy
• Vertical deflection
• Nadir
• Midheaven
• Subsolar point

It has been suggested that this article or section be merged into Celestial coordinate system. ... An old geodetic pillar (1855) at Ostend, Belgium A Munich archive with lithography plates of maps of Bavaria Geodesy (pronounced [1]), also called geodetics, a branch of earth sciences, is the scientific discipline that deals with the measurement and representation of the Earth, including its gravity field, in a three... Man has always been interested in the Earth on which he lives. ... The vertical deflections (deflections of the plumb line, astro-geodetic deflections) are important parameters of the local gravity field. ... For other uses, see Nadir (disambiguation). ... The Midheaven is noted as Mc in this Natal chart, close to the top Ptolemys definition: The Medium Coeli is the point which is upper square from ascendant, eg. ... The subsolar point on earth is where the sun is perceived to be directly overhead. ...

References

• Huschke, Ralph E. (1959) Glossary of Meteorology, American Meteorological Society, Boston, Second printing-1970.
• McIntosh, D. H. (1972) Meteorological Glossary, Her Majesty's Stationery Office, Met. O. 842, A.P. 897, 319 p.
• Picoche, J. (1992) Dictionnaire Etymologique du Français, Le Robert, Paris, ISBN 2-85036-458-4.