The term nadir has several related meanings, primarily coming from astronomy, geography, medicine, and figurative usage:
- In astronomy and celestial navigation , the nadir is the point on the celestial sphere that is directly beneath a specific location or observer ; it is exactly opposite the zenith, which is the point directly overhead. Essentially, the nadir points vertically downward from a location.
- In satellite and remote sensing contexts , the nadir refers to the point on Earth's surface directly below a satellite in orbit. A "nadir view" is when the satellite looks straight down at the Earth providing the most accurate and detailed images.
- In topography , a nadir is a point on a surface that is lower in elevation than all immediately adjacent points—a local minimum in elevation. It can be the lowest point of a basin or the deepest point of a body of water.
- In medicine , the term nadir is used to describe the lowest point of a clinical symptom or laboratory level, for example, the lowest blood cell count a patient experiences during chemotherapy.
- Figuratively, nadir means the lowest point or the worst moment in a situation, such as someone's spirits, career, or a historical period.
Etymologically, nadir comes from Arabic, meaning "opposite to," reflecting its meaning as the point opposite the zenith.
In summary, nadir generally means the lowest point or point directly downward opposite the zenith, with specific meanings varying by context such as astronomy, geography, medicine, and figurative use.
