Re: [meteorite-list] Zig zags and spinning

2004-07-01 Thread GeoZay

zig zagging
Some years ago, I read that the forces necessary to make a fast moving meteoroid have a visual directional change of any kind will immediately destroy it. 
George Zay

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[meteorite-list] Zig zags and spinning

2004-07-01 Thread MexicoDoug
zig zagging
Some years ago, I read that the forces necessary to make a fast 
moving meteoroid have a visual directional change of any kind will
immediately destroy it. George Zay

Wouldn't that be an overly generalized statement, with it's application here? There are enough examples of what looks like, sounds like and feels like "zig zag" (such as the Pasamonte example posted) appearing trails to show it is not completely true.

But the overstatement certainly has some truth in it as well under other conditions. As the bolide spirals or gradually zig zags, odds are that it it sloughing off non-ablated material as it goes along. I would guess that that is the tossed material is specifically at the pressure points which cause the zig zaging to begin with, and from the meteor's point of view is like being hit along the edges with a hammer.

Meteorites recovered on earth are almost always made much smaller than the incoming body principally by this destructive action - right?, and not by smooth ablation which I have no references for, but would suppose accounts for not much more than several centimeters depending on composition and momentum as well. The exceptions are the well oriented pieces.

In studying the changing of direction -"zig zagging"- it is probably important to consider that these changes in direction are cycles are slipped into gradually, not instantly, allowing a much greater disippation of energy. In other words, like the puttering jalopy sounds I mentioned, the entire cycle takes place over seconds, and in the Pasamonte example as well as the one I have researched, the clever choice of words of the Australian witness as "gradual zig zags" which are very noticable, is caused by a rock that spins or tumbles at a relatively gentle rate given the situation, and with each tiny advance in time the overall sheer pressure the rock experiences is basically continuous - tangentially increasing or decreasing in a sense. Should the rock quickly flip or not loose enough momentum, then it might explode in a major way - like Pasamonte eventually did, captured right at that moment after zig zagging, which so enchanted Nininger.

It is worth adding that in space visual changes of direction at meteoritical speeds thankfully are possible, with no problem (Cassini orbital insertion, etc.). Undoubtably your old reference was for meteorite entry into the lower atmosphere. Taking into consideration the exponential nature of the mass distribution (scale height) of the atmosphere, it seems clear that ablation processes dominate meteorites traveling straight as an arrow would (ie, parabolically), removing "cosmic velocity" until the atmospheric soup gets thick and sloughing begins to takes over from ablation for most convient sized meteors. So the zig zagging would be most likely beginning after the initial loss of much momentum, at the lower most visual altitudes for meteors that are interestingly enough most probable to survive as meteorites.

As an after thought, a meteorite which is still smoking and glowing somewhat, creating a smoke trail, at say 1000 miles per hour, that weighs 100 pounds still only needs only a negligable force applied perpendicular to it's entry angle (and moreover, it could be downward) to zig zag. A very noticable zig in the velocity vector, since cosine of up to 8 degrees is over 99% conserved and only affects the momentum (or energy) in this corresponding little bit. Just like a man on a swing really going at it can be pushed laterally by a small child and do (quickly damped by other forces) zig. Or a batter in baseball doesn't even feels the tipping of a fastball yet it goes over the Catcher's head.

And finally, the nice photos - and wood carvings - which appear to have famous bolide families traveling in straight lines - like Peekskill or Newark on Trent. But a good question in those cases, is why they all aren't colinear...clearly something has happened at quite high speed that allowed a change of direction up or down which appreciable-sized fragments survived. There may be a counter argument that they started out as a group. I don't believe that for the majority of those cases. I can't believe small objects in space have much chance of stayying so close together after millions of years. Then there are always the bolides that hit earth at cosmic velocities and manage to "skip" off the atmosphere. It is hard to buy that they hit at perfecty tangents, and the one from California 8 years ago only broke in two - and you know it was going fast as I believe it practically completed one orbit...

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[meteorite-list] Zig zags and spinning

2004-06-30 Thread MexicoDoug
Dear list,

Sounds like we are talking about two different phenoma here: rotational spinning and relative translational displacement, or zig zagging. There is a third one to consider, too, spiraling. Spiraling traces zig zagging in that brief moment of surprise, if like most viewers, they see it from the side, and not coming right at them.

There is no reason the meteorite can't spiral or truly zig zag coming down, something like the random a "skipping" stone a child throws at the water. The same sort of thing happens as the usually rotating meteorite enters the atmosphere. If the rotation is like a steam roller you'll likely get the true zig zag, but if the meteor is irregular enough then you get the two diminsional spiral version of a zig zag. As the amount of surface area to the air changes direction and intensity while rotating, the upward frictional force varies, causing a truer zig zag for the steam roller type spinner, which has one degree less of orientation than a true oriented projectile that fall in a parabolic arc. On the other hand, if the spin axis isn't perpendicular to the incident trajectory (i.e. not a steam roller), you will get a spiral. Either way they look like gradual zig zags.

I have spoken with witnesses to a bolide who independently described the same even as a zig zag in one case, and the other a spiral. They did not have any idea what others reported. They even carefully described to me the sounds accompanying the spiraling cycles: Just like a puttering jalopy which repeats itself every few seconds.

If you're in a speeding car and have the pleasure to stick a "karate chop" hand out the window, held straight out, you can zig zag. If you vary the "straight out" part you will feel the pressure to spiral.

Harvey in "Find a Falling Star" 1972, was very impressed by cowboy Chharles M. Brown's reflexes in capturing the Pasamonte, New Mexico bolide on film on March 24, 1933, at exactly 5:00 PM. Al Mitterling kindly sent me an image of that picture which doesn't appear in the original edition, though it is discussed a lot. I have taken the liberty of posting kind Al's image of Brown's photo at:
where the zig zag is apparent.

Still, I need to agree with Mike in the sense that the newspaper sensationalized the whole thing, saying "a fiery object zigzagging across the sky" when the original actual witnesses' quote is much more appropriate in the same article: "gradual zig zags". There was a slightly suggested, unintention little green men aspect of the reporter's description, in my opinion, too.


Portales Valley was spinning when it fell, so I think that if the body has a
strange angled shape, that it can tumble, or spin while falling, I doubt
that it was zig zagging as in changing directions like they suggest.
Mike Farmer
- Original Message - 
From: "Marc D. Fries" m.fries at
To: "Meteorite Mailing List" meteorite-list at
Sent: Wednesday, June 30, 2004 10:53 AM
Subject: Re: [meteorite-list] Meteor Reported in Australia

 Zig-zagging = tumbling space junk?

  Meteorite reported in southern WA
  Australian Broadcasting Corporation
  June 30, 2004
  The Perth Observatory says it has had reports a meteor has crashed
  near Walpole in Western Australia's south.
  Witnesses say they saw a large, fiery object zigzagging through the
  sky at about 5:30pm yesterday.
  The witnesses say the object left a trail of thick smoke and then
  they heard a bang.
  The observatory says it appears the object was travelling somewhere
  between Perth and Albany in a south-south easterly direction.
  Walpole resident Heather Burton was in her backyard when she saw the
  She says it was unlike a normal shooting star.
  "A shooting star usually just goes straight across or straight down
  - this one had these gradual zigzags just coming down," she said.
  Alex Bevan from the WA Museum says the reports indicate the
  sightings were the result of a fireball generated by a meteorite.
  "We're certainly picking up reports of a bright fireball and sonic
  phenomena associated - I'm absolutely sure - with the fall of a
  meteorite," Dr Bevan said.
  Dr Bevan says it will be difficult to find where the meteorite landed.
  "Unfortunately there doesn't seem to be as many observations, so
  actually pinning down where the object landed might be a bit
  difficult and in that area, the vegetation might mean searching for
  it would be difficult," he said.
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