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 an hour of peak activity, assumed the conditions are excellent (stars visible up to magnitude 6,5). The rate that can effectively be seen is nearly always lower and decreases the closer the radiant is to the horizon. In astronomy, the zenithal hourly rate (ZHR) of a meteor shower is the number of meteors a single observer would see in an hour of peak activity, assumed the conditions are excellent (stars visible up to magnitude 6,5). The rate that can effectively be seen is nearly always lower and decreases the closer the radiant is to the horizon.