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Re: (meteorobs) n, HR, ZHR
Some notes:
If t (or Teff) < 1 hour, you do not have a ZHR. At best, you have an EZHR (estimated ZHR, usually used for high rates in short periods). The statistical meaning of a rate of 671 meteors/hr based on a sample of 50 meteors is limited at best. (But not as limited as 150,000 meteors/hr based on 40 meteors! :)) <--Not meant to be flame bait!
Rates per second or minute are useful in very short, sharp peaks for determining the actual time of the peak, but one must beware of random sampling error as well as observer bias that may create a false impression of high rates in the data, when the average over a statistically significant period would look much less impressive. I have seen 5 Perseids appear simultaneously but would not record an HR of 18,000 for this "storm" because the same hour of observing included periods lasting over a minute where no Perseids were observed. The larger the sample, the more confidence one has in the rates.
Because even at its best (low correction factors and large Teff), a ZHR is an estimate, it is always a good idea to report raw data that includes n, Teff and UT start and end of observing periods, limiting magnitude, geographic location (lat-long), k (% sky obstruction), and a magnitude distribution of the meteors in n (from which r may be calculated with a sufficient sample size). A ZHR can be given along with this, but it's nice to know what the ZHR was calculated from.
Clear skies (please?) and good observing,
Wes Stone
---- you wrote:
> Hello All,
>
> Just to prevent misunderstanding and inaccuracy in reporting the
> upcoming probable Leonids meteor storm.
>
> When reporting ur observational results of meteors, please be accurate
> by specifying whether u r talking about:-
>
> 1- Number of meteors observed within a specific time. (n)
> 2- Number of meteors observed within a specific time AND corrected for
> hourly rate, called "Hourly Rate" (HR).
> 3- Same as 2 but it is corrected for the limiting magnitude, radiant
> elevation, and sky obscureness (by clouds for example). Called "Zenithal
> Hourly Rate" (ZHR).
>
> For example, suppose that u observed 100 meteors from 2:00 Am to 3:00
> Am local time, so u may say that u saw 100 meteors within one hour. But
> if u saw 50 of those meteors from 2:50 - 3:00 (i.e. within 10 minutes),
> then u may say that the (HR) is (50 * 60/10) = 300 meteors per hour !
> While the ZHR which equals to (n * F * c * z / t), where:-
>
> n - number of meteors observed.
> F- Correction for obscureness, which equals 1/k, where k is the
> percentage of the obscured sky.
> c - Correction for limiting magnitude, which equals r ^(6.5-your
> limiting magnitude), where r is a constant for each shower (Leonids r =
> 2.5)
> z - Correction for radiant elevation above the horizon, which equals
> 1/sin (radian's elevation in degrees).
> t - effective observing time in HOURS.
> So in the above example if u observed 50 meteors within 10 minutes, no
> clouds were in the sky, ur limiting magnitude was 6.0, radiant's
> elevation above the horizon was 45 degrees.
>
> So the ZHR = 50 * 1 * (2.5^0.5) * (1/sin45)/ (10/60) = 671 Meteors !
>
> Notice that most observers give their results by ZHR, since it is the
> best to compare ur results with other observers have different
> observational conditions, which will be equalized after applying the ZHR
> formula.
>
> I think many of the observers r aware of what I've mentioned, but I
> just wanted to confirm it, since as u saw during the last 1966 Leonids
> meteor storm's discussion in this mailing list, there was a
> misunderstanding cuz it was not clear whether the 140,000 seen meteors
> at that time is "n", or "HR", or "ZHR".
>
> If u want to know more about ZHR, kindly see one of our observational
> reports at our site.
>
> Full-Meteor Skies :-)
> Moh'd
> --
> **********************************************************************
> Mohammad Shawkat Odeh.
> Jordanian Astronomical Society (JAS).
> Member of JAS Administrative Board.
> P.O. Box 926932 Amman 11110 Jordan.
> odehjas@geocities.com
> http://www.geocities.com/CapeCanaveral/1092/index.html (Personal URL)
> http://www.geocities.com/CapeCanaveral/1092/jas.html (JAS URL)
> **********************************************************************
>
>
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