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(meteorobs) further suggestion for fireball measurements
Hi Folks,
In addition to Ed Majden's excellent summary, I have one further suggestion
to offer with regard to measurements with eyewitnesses of the large NJ
fireball.
That suggestion is to also record for each eyewitness you interview:
1) the angle of the fireball trail with respect to the vertical for the
point of extinction;
...in combination with:
2) azimuth and altitude of that point of extinction.
In addition to this, it is advisable to also record, if possible, the same
points of information (angle and azimuth) but then for the point where the
prolonged fireball trail would cross the horizon. This is easy to do by
having the eyewitness stretch out a cord along the trail path. This
information actually might give best and most straigthforward results.
Last but not least:
3) Also record whether the fireball fell off to the left or right.
The reason for recording all this information is that it, in absence of
multiple video records, is able to yield very sensitive information on the
radiant position of the fireball in the sky, and most notably azimuth of
direction of the path. If you also have speed estimates, that enables you to
calculate an orbit for the fireball/meteorite. We used this method for the
1990 Glanerbrug meteorite fall in the Netherlands and in combination with
trajectory length estimates and speed estimates (from duration), we were
able to get something of an orbit. See the publication in Astronomy &
Astrophysics 255 (1992), 373-376. I recently also employed this method with
sightings of the 1916 Treysa meteorite fall from Germany.
This method actually works best employing sightings from some distance
(hence meteor close to horizon) and spread well around the endpoint.
With regard to time duration estimates: most laypersons estimate much too
long durations. One way to solve this problem is to have an eyewitness
"relive" the event as a "film in memory" starting at a sign made by you
(e.g. a knock on a table) and have him give a signal when the fireball
extinguishes: while you are measuring the duration with a chronometer.
Cheers and good luck!
- Marco Langbroek
Dutch Meteor Society
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Marco Langbroek private: marco.langbroek@wanadoodot nl
Leiden University work: m.langbroek@arch.leidenunivdot nl
Faculty of Archaeology
P.O. Box 9515
http://home.wanadoodot nl/marco.langbroek/dutchmet.html
NL-2300 RA Leiden
The Netherlands
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