(meteorobs) Why do some meteors appear to zig-zag?

[MexicoDoug at aol.com]

Hello Marco, and kindest thanks for your thoughts on the zig zagging question 
(By he way, Lew, too).  For the special cases of bolides entering say, below 
30 kilometers, I would ask you to kindly clarify a few of your thoughts, and I 
want to comment on why I feel the objections you highlight to Pasamonte, 
while certainly valid considerations,  are weak and defective in support of the 
case you make, and perhaps you will consider modifying your interpretation or 
say what is unreasonable in the present assumptions.  With much respect, it 
looks to me as you generalized the whole idea as not believable due to no 
evidence, yet no where do you specifically say why?  How many Pasamonte type fireballs 
do the professionals have to make a clear determination, I wonder.  Since 
that is the special case I support: bolide, high likelyhood to become meteorite, 
and perhaps more friable composition (see below):

I would begin by adding that the Space Shuttle reentry is another interesting 
case in that the energy management system gets switched on at 25 kilometers 
altitude and 2,750 kilometers per hour.  At that speed, I understand zig zags 
(S-turns) are induced by ailerons/rudder to disipate excess momentum, by taking 
advantage of changing the surface area/angle of entry.  That is normal 
operation, and luckily the Shuttle doesn't disintegrate when it changes direction at 
these speeds, and you might probably believe a factor to the tune of 
threefold to cover safety = 8,250 km/hr.  Of course, we are now dealing with "space 
vehicles" which have different density and "porousity", which specifically makes 
them much more vulnerable than falling rocks and irons.  So I do not know why 
it would be surprising that under some conditions, a rock traveling at double 
that speed (yes, even considering frictional resistance may go up as a cube), 
16,000 km per hour couldn't make it's own S turns based on the sloughing and 
ever changing effective entry angle and area from tumbling (sloughing you did 
recognize and called fragmentation). 

Further, as a few others have pointed out and you yourself concurred, high 
speed bifurcation which includes visual changes in direction do happen!  When I 
brought it up, it was to justify directional changes due to energy of the 
system  I don't want to open the meteor zig zagging can of worms, as I tend to 
agree with you that typical meteors don't zig zag noteably, unless they happen to 
split.  (But I'm quite open to special circumstances which would)

Back to bolides, I mentioned in a post that anything up to a highly visual 8° 
change in direction should require less than 1% of the total momentum.  So 
for the case of a body that throw's off material we should expect a change in 
direction.  The periodicity of such emissions  might be very subject to 
question, but the ability to creat a zig, I would say, not.  Then the rotation - 
finding the axis favored by resistance, just a a modern windmill finds it---and 
continues to rotate based on enery considerations-- would have to be the 
principal driving force.  Also, if we unbalanced the air resistance on a modern 
windmill by modifying a blade, there is a nice possibility it might whistle for us 
with a relatively constant period, though perhaps varying tangential velocity.

A comment I believe you (perhaps it was someone else, can't remember) made on 
Pasamonte, was that it was a Eucrite.  That could use further development, I 
think, as I also believe (reasonably, I hope) that such relatively fragile 
rocks are more likely to slough off material.  As a matter of fact, an even more 
friable incoming candidate meteorite, I would expect to continuously slough as 
I described in the earlier posts.  Perhaps irons and H-L-LL types are much 
more likely to make it in whole...just a comparison of recovered fusion crusted 
samples should give enough evidence on which is most vulnerable.

Now for my inconformity to the Pasamonte objections you have, which is not 
inconsequential, by the way, as it it a true data point requiring analysis, and 
the fact that a cowboy took it in 1933, and not NASA or a professional survey, 
is inconsequential, if not downright humorous.  I do not know how long the 
exposure was in that photo.  But the two objections you mention seem weak at 
best, and more likely defective to me:

  >>"The often quoted evidence of of the Pasamonte fireball is 
inconsequential, 
  >>as many feel this photograph is:
  >>1) motion blurred (it was taken out of the hand with a long exposure, not 
from a tripod)

Perfectly timed comment.  First, if this were true, and so were 2), we would 
not see a smooth progressively downward spiral with three of four relatively 
uniform periods..  We would see a smeared trail up and down - but we only see 
an nice continuous "tubular" train.  So at least one of these two would appear 
to be in error.  Perfectly timed because, did you see the "video" just kindly 
posted of the Shreveport-North Texas bolide, or whatever it is?  Did you 
notice what sort of pattern a time exposure there would do - or alternatively, 
imagine photographing a Planet or an airplane with your own handheld camera and 
coming up with such a smooth spiraling regular period-pattern.  One can also 
look at the "zig zag" produced.  I don't know where the horizon is, but if it is 
horizontal too in the image, it suggests that the spiral is continuously 
coming down - one would expect at least one movement make the appearance of an 
"upward" zig.  

  >>2) shows the persistent train, not the fireball as often claimed.

If this were true, then 1) would be completely false and I believe ruled out. 
 The whole trail would be victim of the zig zagging.  A little inspection of 
the image, seems to show the explosion of the main mass as a nipple in front 
of the ellipse on the leading light.  That little nipple would immediately 
throw suspicion on option 1), and prove option 2) wrong.
Finally, what I can add regarding the circumstances of the photo seems to 
rule out this possibility strongly.

>From Dr. Nininger's book discussing the photo:
"Charlie told me that he habitually kept his camera on the radio cabinet near 
his chair at the breakfast table.  He described matter-of-factly how the 
unearthly light turned everything into mid-day, and he simply grabbed the Kodak 
and dashed outside, opening it as he ran, pointed it, and snapped the shutter.  
Then he wound the film and tried for another shot, but the second one was not 
good; he believed the light was too intense after the bursting of the big 
fireball."
I had him reenact the scene for me, timing him carefully.  The entire 
sequence required eight and one half seconds,, an interval that was consistent with 
other reports that the fireball was visible for fifteen to twenty two seconds.

While one could say the running caused objection 1) I think the above helps 
preclude that, and further, if we are to believe the brightest light being 
after the photo, it is clear that the first photo would have been of the flight of 
the meteorite- since it was "before bursting".

I have no special tie or interest to this photo, nor debated this point 
before.  It may in fact have some defect.  But, the defects claimed from 1) and 2) 
seems surprisingly obviously no good, inconsistent with each other, and 
individually as well.  That leaves weather pattern argument.  It is hard to justify 
the brightness in an age of nascient photography of the far end of the trail, 
and that somewhat random wind patterns would creat such nice patterns withough 
smearing the tubular shape somewhat, or adding at least just one single sharp 
angle deviating for the path, or at least a variation in particles - 
additionally - what a coincidence that the projection of the spiral angles are so 
similar.  I don't think the winds are so intent on fooling us....


  >>I recently summed it up for A/CC ( 
http://www.hohmanntransfer.com/mn/0405/27.htm#snmet)
  
Hope that helps.  Marco never come out and disagree, but the tone suggests 
you dismiss that photo and the whole idea of zig zagging, in spite of the 
momentum, sloughing, varying area arguments.  I find it personally much harder to 
believe that under the right conditions the couldn't and doesn't happen.  Then I 
add it to the witness accounts I have for a spiraling bolide, complete with 
type of sounds, and one person who actually saw the nucleus itself spiraling as 
it passed overhead, among others out of contact with them, who related 
similar stories --- down to matches of color, angles, etc., on that one example, 
I've heard enough to start believeing I saw it if I'm not careful.  But no one 
had any fireworks here nor anything else to do, and the best witness watched it 
practically whiz over his head (yes, I triangulated it independent of his 
observation to know this is true) really didn't have much else to do, so this is a 
case of a spiraling, smoking, bolide without doubt.  If it is typical of one 
of 100 or one of 3, I can't know and hopefully the professional watchers can  
sort that out...

Saludos,
Doug


En un mensaje con fecha 07/07/2004 4:06:12 PM Mexico Daylight Time, 
marco.langbroek at wanadoo.nl escribe:

> 
> I do not believe in zig-zagging meteors at all. I do not know of ANY 
> fireball photographed by the professional meteor surveys, that zig-zags on the 
> image.
>   
> By contrast, persistent trains and dusttrails in the wake of a bolide start 
> to show zig-zag or corkscrew patterns sometimes within seconds of trail 
> formation. This is due to high altitude winds. I think that many reports on 
> 'zig-zag' meteos are influenced by (inexperienced) observers noting the corkscrew 
> persistent train/dust trail, and then thinking the meteor itself must have 
> zig-zagged to form the trail.
>   
> The often quoted evidence of of the Pasamonte fireball is inconsequential, 
> as many feel this photograph is:
>  1) motion blurred (it was taken out of the hand with a long exposure, not 
> from a tripod)
>  2) shows the persistent train, not the fireball as often claimed.
>  I recently summed it up for A/CC ( 
> http://www.hohmanntransfer.com/mn/0405/27.htm#snmet)
>   
> - Marco
>   
> ------
> Dr Marco Langbroek
> Dutch Meteor Society (DMS)
> Leiden, the Netherlands
> 52.15896 N, 4.48884 E (WGS 84)
>   
> 

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