MAA Glossary

N


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.