John S. Mathis
Contributor
LOCATION: Madison, WI, United States
Professor of Astronomy, University of Wisconsin, Madison.
Primary Contributions (8)
Nebula, any of the various tenuous clouds of gas and dust that occur in interstellar space. The term was formerly applied to any object outside the solar system that had a diffuse appearance rather than a pointlike image, as in the case of a star. This definition, adopted at a time when very…
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