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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| Exosphere |
The outermost tenuous layers of a planetary atmosphere, which merge into the interplanetary medium. In this region, the density is so low that very few collisions occur between the atoms, and atoms moving rapidly are able to escape from the gravitational pull of the planet. The Earth’s exosphere starts at a height of about 400 to 500 kilometres 250 to 300 miles.
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