Zenithal Hourly Rate

In astronomy, the Zenithal Hourly Rate (ZHR) of a meteor shower is the number of meteors an observer would see in one hour under a clear, dark sky (limiting apparent magnitude of 6.5) and if the radiant of the shower were in the zenith. The rate which can effectively been seen is always lower and decreases as the radiant is closer to the horizon. See also List of meteor showers