Nadir

Nadir is the point on the celestial sphere directly beneath an observer, the exact opposite of the zenith, which is the point directly overhead. If you could draw a straight line from your head, through your feet, and continuing all the way through Earth and out the other side into space, the point where that line meets the sky on the far side would be the nadir. In everyday stargazing, the nadir isn't something you can look at directly, since it lies below the horizon and through the ground, but it is a genuinely useful reference point in astronomy and navigation for defining a complete coordinate system: together, the zenith and nadir mark the two poles of an observer's local sky, with the horizon forming the great circle exactly halfway between them. The term also appears in remote sensing and satellite imaging, where a satellite's nadir is the point on Earth's surface directly below it, and "looking at nadir" means pointing an instrument straight down rather than at an angle — a common way Earth-observing satellites capture consistent, distortion-minimized imagery of the ground beneath their orbital path.