Nebula------------------------------------------------
Originally, the word "nebula" referred to
almost any extended astronomical object
(other than planets and comets).
The etymological root of "nebula" means "cloud".
As is usual in astronomy,
the old terminology survives in modern usage
in sometimes confusing ways.
We sometimes use the word "nebula" to refer to galaxies,
various types of star clusters
and various kinds of interstellar dust/gas clouds.
More strictly speaking,
the word "nebula" should be reserved for gas
and dust clouds and not for groups of stars.
--information taken from web--
--information taken from web--
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