[Prev][Next][Index][Thread]
(meteorobs) Calculating Mt.Lemmon Leonid ZHR (was Leo 2001 coverage in S&T 3/2002)
Ed Cannon wrote:
> I beg everyone's pardon, but I'm still not getting something
> about the fine points of ZHR calculation as it seems to be
> presented by our experts.
You have neglected the limiting magnitude. THe ZHR is defined at +6.5.
If conditions are better than that, i.e. the LM is fainter than
+6.5---highly likely for a mountain in the leading US mainland state for
professional observatories---observers will on average see more meteors
per unit time. The exact correction depends on the relative numbers of
meteors at different brightnesses. Under premier conditions this
might halve the ZHR, and a 25% reduction is not implausible for
Mt.Lemmon.
Then there is the observer's perception. Some of us are better than
others at detecting meteors. It's quite possible in a small group for
all the observers to be above average perception, whereas as the ZHR is
for the `average' observer. IMO determines these relative performances
from comparing observations by many observers, and individuals are
assigned a perception factor. This factor applies a correction to the
observer's estimated limiting magnitude.
Then there are statistical variations in the activity from site to site.
Given the larger numbers this is less of a factor proportionally than
the first two factors given above.
Groups also disagree on the correction factor for the radiant elevation.
If you can combine observations at the same UT, for different radiant
elevations, the effect of the different factors are reduced.
> same hour from the same location must be considered, but it
> still seems to me that the higher actual count must set a
> minimum constraint on the actual ZHR.
This is an invalid premise in Ed's argument.
Malcolm Currie
The archive and Web site for our list is at http://www.meteorobs.org
To stop getting all email from the 'meteorobs' lists, use our Webform:
http://www.meteorobs.org/subscribe.html
References: