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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| Second |
A unit of time measurement defined in the International System of Units Système International, or SI as the duration of 9,192,631,770 cycles of radiation corresponding to the transition between two hyperfine levels of the ground state of the caesium 133 atom.
See also: arc second.
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