Nadir Nadir The nadir (, ; from / ALA-LC: "naẓīr", meaning "counterpart") is the direction pointing directly "below" a particular location; that is, it is one of two vertical directions at a specified location, orthogonal to a horizontal flat surface there. 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 the nadir is the zenith. Nadir is
Nadir also used figuratively to mean the lowest point of a person's spirits, or the quality of an activity or profession. In medicine, the term nadir is used to represent the lowest level of something being measured; for example, of a blood cell count while a patient is undergoing chemotherapy, or of a blood glucose level after a baby is born. A diagnosis of neutropenic nadir after chemotherapy typically lasts 7–10 days, and a newborn's blood sugar normally reaches its nadir around 2 hours after birth. The word also refers to the downward-facing viewing geometry of an orbiting satellite, such as