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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| Zenithal Hourly Rate Zhr |
The hypothetical rate at which meteors of a particular meteor shower would be observed by an experienced observer, watching a clear sky with limiting magnitude 6.5, if the radiant were located in the zenith. The lower the altitude of the radiant, the lower the observed rate. To a first approximation the ratio of the observed rate to the zenithal rate is the sine of the altitude angle of the radiant.
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