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(meteorobs) Re: [IMO-News] eta Lyrids




NOTE: Again, Marco is not a 'meteorobs' subscriber. Please be SURE to "Cc:" his
address 'marco@rulpre.LeidenUnivdot nl' in any replies you send on this thread!

Lew Gramer <owner-meteorobs@jovian.com>

------- Forwarded Message

To: imo-news@egroups.com, molau@informatik.rwth-aachendot de
Cc: marcolan@stad.dsldot nl
From: "Marco Langbroek" <marco@rulpre.LeidenUnivdot nl>
Date: Mon, 15 May 2000 17:28:43 +0100
Subject: Re: [IMO-News] Re: eta Lyrids

Sirko wrote:
 
> Maybe you misunderstood me: I was not going to say that what the visual
> observers saw was an illusion.
> Carl and Rainer asked me to check whether I
> find these eta Lyrid meteors in my video data. I did that, but I found not
> a single member in these two nights even though the geometry was quite
> favourable, i.e. I observed at only little distance from the
> supposed radiant.
> Our video data have helped to examine the true nature of the 'xi Bootids',
> for example, but in this case we seem to have less fortune. That's all I
> wanted to let you know with my previous posting


Hello Sirko,

I got a bit stingy because whenever video data enter the field people 
seem to tend to jump to the conclusion that these settle the issue. 
That's not your fault of course, but still it is what happens. In 
some cases, video indeed has done a fine job. But video also 
has its drawbacks, and there is the matter of sample size. Video 
observations just do not necessarily overrule visual reports just 
because they are from video cameras instead of humans that can err.
In the case of eta Lyrids, which are  a minor stream (which means: 
few meteors, also for video cameras), and a stream actually 
observed now for several years (this years observations are not the 
first mentioning of the stream), I really don't think 50 sporadic video 
meteors among which you expect few members of a minor stream like 
this have much to say. Your intro to your mail  (actually, I was not even aware 
of the
'discussion' you mentioned expect for 2 of the the private mails between Carl, 
Rainer and you I got) and its content did suggest to me that your 
data should imply that there has most likely been no true activity;
and this made me stingy simply because as mentioned I have noted that 
there is a tendency to take whatever has "video" involved as very decisive and 
unproblematic, notwithstanding the fact that video cameras can also 
suffer from low sample sizes (just as do visual observers of 
course!), are biased in recording streams with differing population 
indexes, and nothwithstanding that transforming video records into 
real flux rates is so far still problematic.

In the current context, I thought I should remind people of that. Not 
because I think video would have little to say (actually, I think 
video is one of the most informative new techniques that arrived 
last 15 or so years within meteor observing and should be taken very 
serious. At the same time, I urge video explorers not to get into the 
trap of becoming too overconfident in their technique. The discussion 
on the "drop-off" in the fainter portion of the Leonid magnitude 
distribution is a case at hand. I really think video failed there and 
possible detection bias by the cameras  and recording technique was 
not properly taken into account), but because I feel that sometimes video data 
are presented too uncritically as 'unproblematic', or at least are 
too often taken as such by the 'consumers' of video reports. Every 
technique has its drawbacks and problems and that should be acknowledged.

Allright, I've made my point I guess. It has been a long warm day 
here.... So lets cool down this discussion.

Marco

- ----------------------------------------------------------
Marco Langbroek
Faculty of Archaeology      tel. +31 71 5272930/25
Leiden University           fax  +31 71 5272928
P.O. Box 9515               m.langbroek@arch.leidenunivdot nl
NL-2300 RA Leiden
The Netherlands
- ----------------------------------------------------------

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