This section is from the book "The Home Cyclopedia Of General Information", by Charles Morris. Also available from Amazon: Home Cyclopedia of Necessary Knowledge.
A vapory patch of seemingly gaseous matter seen in the heavens among the stars, and sometimes of immense dimensions. Many of the supposed nebulae have been shown to be clusters of very distant stars, but others are proved by the spectroscope to be made up of luminous gas. Great numbers of them exist.
 
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