Zenithal Hourly Rate
In
astronomy, the
Zenithal Hourly Rate (ZHR) of a
meteor shower is the number of meteor 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 decrease as the radiant is closer to the
horizon.
See also List of meteor showers