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(meteorobs) n, HR, ZHR

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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