Nadir

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

The nadir (from Arabic نظير nathir, "opposite") is the direction pointing directly below a particular location (perpendicular, orthogonal). Since the concept of being below is itself somewhat vague, scientists define the nadir in more rigorous terms. Specifically, in astronomy, geophysics and related sciences (e.g., meteorology), the nadir at a given point is the local vertical direction pointing in the direction of the force of gravity at that location. The direction opposite of the nadir is the zenith.

Nadir also refers to the downward-facing viewing geometry of an orbiting satellite^[1], such as is employed during remote sensing of the atmosphere, as well as when an astronaut faces the Earth while performing an EVA.

This diagram depicts a satellite observing backscattered sunlight in the nadir viewing geometry.

The word is also used figuratively to mean the lowest point of a person's spirits. ^[2]

[edit] See also

• Zenith

[edit] References

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