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.
Assignment given to an object listed by number in Dreyer's New General Catalogue of Nebulae and Clusters of Stars.
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.
A star that explodes, temporarily increasing its brightness 100000 or more.
A nodding motion of the earth's pole superposed on the slow precession.