Nadir

In astronomy, the nadir is the point directly beneath your feet on the celestial sphere, opposite the zenith, which is directly above your head. Imagine looking straight down from your position; that spot on the sky underside is the nadir. It helps astronomers and navigators describe precise locations relative to an observer's position on Earth. Essentially, the nadir is a reference point indicating the lowest point in your field of view, directly beneath you, relative to the sky or celestial objects.