Zenith

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Diagram showing the relationship between the Zenith, the Nadir, and different types of Horizon. Note that the Zenith is opposite the Nadir.
Diagram showing the relationship between the Zenith, the Nadir, and different types of Horizon. Note that the Zenith is opposite the Nadir.
HORIZONTAL COORDINATES. Azimuth, from the North point (red) -also from the South point toward the West (blue). Nadir is in the opposite direction, south. Altitude, green.
HORIZONTAL COORDINATES. Azimuth, from the North point (red) -also from the South point toward the West (blue). Nadir is in the opposite direction, south. Altitude, green.

Zenith is the direction pointing directly "above" a particular location; that is, it is one of two vertical directions at the location, orthogonal to a horizontal flat surface there.

The concept of "above" is more specifically defined in astronomy, geophysics and related sciences (e.g., meteorology) as the vertical direction opposite to the net gravitational force at a given location.

The opposite direction, i.e. the direction of the gravitational force is called the nadir. The term zenith also refers to the highest point reached by a celestial body during its apparent orbit around a given point of observation. This sense of the word is often used to describe the location of the Sun, but it is only technically accurate for one latitude at a time and only possible at the low latitudes.


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