What does ZHR: mean

[Pinwheel (Doug)]

What does ZHR mean. it cant' be Zero hour because the reference is ZHR:100

Perseid Meteor Shower
Starts Jul 17
Peaks Aug 13
Ends Aug 24
ZHR: 100
Speed: 59 km/s
Radiant: RA: 03:04 Dec: 58°

Thanks,

[renormalised (Carl)]

ZHR=Zenith Hourly Rate, or the number of meteors you see pass directly overhead in one hour.

[erick (Eric)]

And ZHR:100 means it could be a good show! If you are observing from the right spots on the Earth

[Pinwheel (Doug)]

So it should be MPH:100 Meteors per hour then

[renormalised (Carl)]

Originally Posted by erick

And ZHR:100 means it could be a good show! If you are observing from the right spots on the Earth

Yeah, better than average

[renormalised (Carl)]

Originally Posted by Pinwheel

So it should be MPH:100 Meteors per hour then

No, not quite. You could get more than 100 per hour if you looked across the whole sky, but you might be seeing the results of optical illusions and not true meteors (i.e. a mirage type of situation with meteor trails at a long distance being refracted through the atm'), so they take a count of those directly above the observer's head to get a better idea of how many are actually passing through the spot where the observations are occurring. That way, you get a more accurate count of how dense the trail is and hence the numbers of meteors present in the trail.