N

Nadir

The point on the celestial sphere diametrically opposite to the zenith.

 

Node

Either of the points on the celestial sphere at which the plane of an orbit intersects a reference plane. The position of one of the nodes (the longitude of the ascending node) is traditionally used as one of the standard orbital elements.

 

Nutation

Oscillations in the motion of the rotation pole of a freely rotating body that is undergoing torque from external gravitational forces. Nutation of the Earth’s pole is specified in terms of components in obliquity and longitude.