Nadir is employed during remote sensing of the atmosphere, as well as when an astronaut faces the Earth while performing a spacewalk. The term nadir can also be used to represent the lowest point reached by a celestial body during its apparent orbit around a given point of observation. This can be 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. The sun is said to be at the nadir at a location when it is at the zenith at the location's antipode
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