(astronomy) A dark nebula; a diffuse mass of interstellar gas and dust that absorbs all incident radiation without reemission.

(astronomy) A nebula composed of ionized gases which produce visible light (as distinct from a reflection nebula, which reflects the light produced by neighboring stars).

plural of dark nebula

plural of emission nebula

plural of radio nebula

plural of spiral nebula

(astronomy) A planetary nebula in Gemini, Milky Way Galaxy

(astronomy, obsolete) The Andromeda Galaxy, a term that was used before it was known to be a spiral galaxy.

plural of planetary nebula nucleus

(astronomy) The remnant hot luminous core of the stellar progenitor of the planetary nebula, which ionizes the surrounding planetary nebula.