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天頂出現数
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Wikipedia definition
1. Zenithal Hourly Rate​In astronomy, the Zenithal Hourly Rate (ZHR) of a meteor shower is the number of meteors a single observer would see in one hour under a clear, dark sky (limiting apparent magnitude of 6.5) if the radiant of the shower were at the zenith. The rate that can effectively be seen is nearly always lower and decreases the closer the radiant is to the horizon. The formula to calculate the ZHR is: where represents the hourly rate of the observer.
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