Re: (meteorobs) Nov 15/16 Leonid Observations

At 04:12 PM 11/16/99 EST, you wrote:
>Call my silly, call me uninformed, but why are everyone's observations so 
>much different from the rates listed on 

A compliment to Dr. Wlasuk's words:

There are three reasons for the rate discrepancy:

1.  The NASA web site is reporting corrected Zenith Hourly Rates (ZHR's).
A radiant altitude of 30 deg will cause a factor of 2 difference between
observed and corrected rates, while a radiant altitude of 15 deg will cause
this correction factor to be 4 or so (under perfectly dark, clear skies).
Additional correction factors for limiting magnitudes, field of view, and
so on will create an even larger difference.

2.  The NASA teams are using a video system, along with their visual
observers, to calculate ZHR's from, and these will have a rather different
instrument response and magnitude sensitivity as compared to a human observer.

3.  Many of the reports sent in to NASA from the amateur astronomy
community are not from experienced meteor observers, and might be subject
to some sporadic contamination, etc.  

Also note that all reports to date, from all sources, are quite preliminary
in nature, and are not, therefore, carefully screen, fully evaluated rates
and profiles.  They are primarily meant to give the general public and
satellite operators a good "quickie" view of what is going on, so they can
make operational decisions as the shower progresses.  The detailed analysis
will come later on.

BTW;  The AMS 1999 Leonids Update page, located at:


is attracting a good many hits per day now.  Many thanks to all of you who
have been sending in reports and narratives for this effort.  The better I
can keep myself informed about what is going on out in the field through
your reporting efforts, the better i can keep the general public and
astronomy community informed about how the Leonids are progressing.

Best regards,


James Richardson
Department of Physics
Florida State University (FSU)

Operations Manager 
American Meteor Society (AMS)
To UNSUBSCRIBE from the 'meteorobs' email list, use the Web form at: