(meteorobs) The Perseids of 1991-1994 - so what *were* the maximum ZHRs?

Marco Langbroek marco.langbroek at wanadoo.nl
Sat Aug 12 05:59:43 EDT 2006



Daniel Fischer wrote:

> There is also a cryptical statement in § 3.1: "The reported rates by Brown & Rendtel were
> corrected by +15 per cent in order to match the ZHR scale of Jenniskens" - I thought the
> ZHR formula was clearly defined

Hi Danniel,

No. There is no such thing as "the" ZHR formula. Factors in versions of the 
formula are under discussion. For example, use a gamma exponent of 1.0 or 1.4 
for radiant altitude correction? How exactly is the r-value defined? Some 
versions employ calibration of individual observer rates to a standard observer 
(the Cp factor), some don't.

> and without personal fudge factors? 

The difference is largely in the gamma value in radiant altitude correction. IMO 
uses 1.0, DMS 1.4.

The DMS method (the one Peter J. employs) also makes use of a calibration of 
individual observers to a "standard" observer, defined as one that would see 10 
sporadics/hour in mid August around local midnight with Lm at +6.5.

There are also differences in te r-value definition.

All together, the effect is that IMO ZHR's are usualy a factor 0.15 to 0.25 
higher than DMS ZHR's

 > And how do you define 'ZHR max'
> anyway: How much and precisely how are the counts smoothed?

I think Peter J. uses trendline fits to the unsmoothed data (as did I when I 
still made active analysis) to determine peak levels.

- Marco

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Dr Marco Langbroek
Dutch Meteor Society (DMS)

e-mail: meteorites at dmsweb.org
private website http://home.wanadoo.nl/marco.langbroek
DMS website http://www.dmsweb.org
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