Nebula, dark:
A cloud of dust and gas, seen in silhouette against a starry background of the
Milky Way.
Nebula, gaseous diffuse (gn):
Irregular cloud of glowing gas and dust, deriving its luminosity from nearby
hot, bright stars.
Nebula, planetary (pn):
A glowing, roughly spherical gaseous object, which may be the remains of an old
nova.
NGC:
Assignment given to an object listed by number in Dreyer's New
General Catalogue of Nebulae and Clusters of Stars.
Node:
Point where the orbit of a planet, as viewed from the sun, intersects the
ecliptic. The ascending and descending nodes refer respectively to the points
where the planet moves from S to N and N to S.
Nova:
A star that explodes, temporarily increasing its brightness 100000 or more.
Nutation:
A nodding motion of the earth's pole superposed on the slow precession.