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Re: (meteorobs) Re: The Leonid Meteor Outburst of 1997

Hi -- thanks for your comments about the use of video to count meteors.
While it is certainly true that the field of view of the human eye is
greater than that of the  video cameras we discussed, the low-light video
cameras are far more sensitive to the quantity "meteors per steradian."
Consider the geminid shower you observed.  If you divide the number of
meteors you counted visually by the field of view in square degrees, you
will probably find that it is a lower number than the same ratio for the
video camera. Of course, in the case of showers that might be dominated by
bright meteors (the 1998 Leonids perhaps?) the human eye could win by
virtue of its greater field of view. When the magnitude distribution is
dominated by faint meteors, a video camera with 6+ limiting magnitude and a
reasonable field of view is likely to be superior. 

I would also note that there is no easy way to distinguish between a single
larger meteoroid that fragmented high in the atmosphere vs. a tightly bound
clump of tiny meteoroids in an orbit roughly matching Tempel-Tuttle's from
the data we have at our disposal for the 1997 outburst.

In either case, you are correct that the mini-outburst of 1997 is not
related in a meaningful way to the great Leonid storms of the past, except
that the excellent video does hint at what a real outburst might be like
for those of us who haven't seen one first-hand. 

Regards, Tony Phillips

>This contradicts my own experience. Two years earlier I recorded the
>Geminid maximum from Germany with an intensified video system that had the
>same field of view (20 deg), but a much better limiting magnitude of about
>8.5 mag for stars. My personal lm was something around 6.2, but visually I
>recorded more than twice as much meteors in less effective observing time.
>Looking at the number of shower meteors this ratio becomes even worse for 
>video, since the smaller your field of view, the fainter the average
>meteor you record and the lower the percentage of shower meteors. So far
>there has been no occasion that my image intensified camera recorded more
>meteors than me - neither during several Perseid or Leonid, nor during
>this Geminid campaign!
>
>> The video cameras atop Mauna Kea in 1997 saw about 150 meteors in less than
>> 2 seconds. That corresponds to an hourly rate of 180,000 - 270,000 per
hour,
>> which is comparable to the activity seen over western North America during
>> the great Leonids meteor storm of 1966. 
>
>This comparison makes no sense at all: If I observe a meteor, I just have
>make the observing intervall very small (say 0.01 second) and immediately
>I have "stormlike rates". The event of Kinoshita was probably one big
>meteoroid desintegrating before entering the atmosphere (as suggested in
>the paper), thus it has nothing to do with the great meteor storms of the
>19th and 20th century.
>
>BTW, in connection with meteor storm we do not use the term ZHR (zenithal
>hourly rate) but EZHR (equivalent ZHR) to underline the fact, that the
>duration is much shorter than one hour.
>
>Best regards,
>Sirko Molau
>
>----------------------------------------
>Sirko Molau -- Video Commission Director
>International Meteor Organization
>e-mail: video@imodot net
>WWW   : http://www.imodot net/video
>----------------------------------------
>
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>
====================================================
Dr. Tony Phillips        phillips@spacesciences.com

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