Space exploration began with the launch of Sputnik and Astrophysics was born as the application of physics to the phenomena observed by Astronomy, which etymologically means laws of the stars.
There are 2759 entries in this glossary.| Term | Definition |
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| Gaseous Nebula |
A glowing cloud of gas in interstellar space, which may be either an emission nebula or a reflection nebula. The expression used to be employed more often, when galaxies were referred to as extragalactic nebulae, in order to emphasize the distinction. The adjective gaseous is now generally omitted since nebula is normally used only for such interstellar clouds and not for galaxies.
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