[meteorite-list] A Twisted Meteor Trail Over Tenerife

[Meteorites USA]

Hi Rob, Sterling, List,

I think you might be right... ;) I might be able to answer my own 
question. I enhanced and enlarged the image on my computer. The stars 
aren't squiggly because they're bigger. If that makes sense. The stars 
don't move across the plane of view as much as the meteoroid during the 
1 minute exposure. A "Bump" to the tripod during this exposure would 
make the stars appear larger as the wobble of the camera allows the star 
to move in a back and forth pattern until the camera stops moving, 
making the stars appear as slightly larger. If you zoom in to 500X, 
you'll notice a kind of half halo around most of the larger stars 
suggesting the camera moved during the exposure, and the smaller stars 
don't seems to be the round points of light they should be, and are in 
fact linear streaks of light..

Back to the meteor. The meteor moved across the frame's plane of view, 
basically covering more distance across the frame than the stars. Bump 
the camera just a little, and I can see where this would make the meteor 
trail appear to spiral/zig-zag. Add in the fact that it tapers toward 
the end into a straight line would correspond to the motion of the 
camera settling back to a stationary position.

Occum's Razor in effect... I stand corrected.

Bump...

Regards,
Eric


On 6/2/2010 3:47 PM, Matson, Robert D. wrote:
> Hi Eric,
>
>    
>> ... physically speaking isn't the image explainable by an oblong or
>> asymmetrical meteoroid tumbling through the atmosphere then twisting
>> into a spiral by the aerodynamic forces exerted on it. Not unlike a
>> curve-ball thrown by a pitcher?
>>      
> If a physical object were moving like this, it would be experiencing
> forces far greater than the deceleration due to atmospheric drag --
> forces which no small meteoroid could survive. You have to appreciate
> the magnitude of the transverse motion required by the meteoroid to
> produce that amount of "squiggle" at a range of 300+ km. You're talking
> a kilometer, maybe more -- PER oscillation. If the meteoroid is
> spiraling in, it's completing a circle of radius 500 meters in perhaps
> a tenth of a second. That means a velocity of ~30 km/sec (on top of the
> forward velocity of the meteoroid), which corresponds to an angular
> acceleration of 1800 km/sec^2. That's over 180,000 G's.
>
>    
>> The only question I had was the frame rate/shutter speed at which this
>> image was captured... If the image frame was taken in 1/25 of a
>>      
> second,
>    
>> there a big difference in the elapsed time between a five minute
>>      
> exposure,
>    
>> which this image does not seem to be from. So I looked it up...
>>      
>    
>> The data from the image states:
>> Canon EOS 20D
>> Shutter Speed: 1.0 (meaning 1 second, not one minute)
>>      
> No, this was a 1-minute exposure.  (The easy visibility of the Milky Way
> in the fisheye image should be enough to convince anyone that this was
> not a 1-second exposure.)
>
>    
>> If the camera/tripod was bumped or jarred during the exposure please
>> explain why ALL the stars in the photo aren't "squiggly" too. Only
>> the smoke train is.
>>      
> No, the stars are too -- it's just that you can only notice it with the
> brighter stars. The reason for that is that the duration of the mount
> vibration was probably only a couple seconds before it completely damped
> out. So you have 58 seconds of stationary integration, and 2 seconds of
> oscillating integration -- roughly a 30:1 ratio.  If the limiting
> magnitude of the image is, say +7, then only stars brighter than
> about magnitude +3.5 will show the vibrational smear.
>
> --Rob
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