Celestial Point is a term used to describe the three points in space that are used to measure the position of a celestial body. The first point is NADIR, which is the point on the celestial sphere directly below an observer. The second point is APOGEE, which is the point in the orbit of a celestial body that is farthest from the center of its orbit. The third point is APEX, which is the point in the orbit of a celestial body that is closest to the center of its orbit.