Nadir

Nadir also refers to the downward-facing viewing geometry of an orbiting satellite,[2] such as is employed during remote sensing of the atmosphere, as well as when an astronaut faces the Earth while performing a spacewalk.

A satellite ground track represents its orbit projected to nadir on to Earth's surface.

Generally in medicine, nadir is used to indicate the progression to the lowest point of a clinical symptom (e.g. fever patterns) or a laboratory count.

In oncology, the term nadir is used to represent the lowest level of a blood cell count while a patient is undergoing chemotherapy.

[4]The word is also used figuratively to mean a low point, such as with a person's spirits,[5] the quality of an activity or profession,[6] or the nadir of American race relations.