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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| Nebulium |
A hypothetical element, the existence of which was postulated in the nineteenth century to account for unidentified emission lines in the spectra of some luminous nebulae. It is now known that these lines are attributable to known elements, but they are not usually observable under laboratory conditions. For that reason they are described as forbidden lines by physicists.
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