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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| Expanding Universe |
A model of the universe in which the fundamental length scale increases with the passage of time. The separation between clusters of galaxies would today be considered an appropriate length scale for this purpose.
The discovery that the redshifts of galaxies increase with distance 1929 and the detection of the cosmic background radiation 1964 are generally taken as evidence that the universe is expanding.
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