[meteorite-list] A Twisted Meteor Trail Over Tenerife

From: Göran Axelsson <axelsson_at_meteoritecentral.com>
Date: Thu, 03 Jun 2010 11:15:16 +0200
Message-ID: <4C0772A4.4050204_at_acc.umu.se>

Sterling, I don't agree with your calculation of the cycle time.

Most meteor trails are very short in time, often sub-second based on my
experience. So even if the exposure was 59 seconds the trail only lit up
for a very short time. Therefore the vibration does not have a period of
7-7.5 seconds. It probably have a frequency around 10-20 Hz. A signature
of a stiff mechanical system like a camera tripod.

My guess is that it is a bump.

/G?ran

Sterling K. Webb wrote:
> Rob, Eric, List, etc.
>
> If there was a "bump" during the last few seconds of
> a 1-minute exposure, the exposure of the right-most
> 97% of the trail would be 97% complete -- and straight.
> Only the left end would be "wiggled." Wiggling of the
> right end would be very, very faint, if visible at all.
> Not a bump.
>
> However, the sinusoidal "motion" can be traced back
> to the start of the trail. There are slightly more than
> 8 full cycles recorded, each of increasing amplitude.
> This yields a period between 7.0 and 7.5 seconds
> per cycle.
>
> Such a frequency combined with increasing amplitude
> could be attributed to vibration from machinery starting
> up, like that found in observatories (where the photo
> was taken). But I think it's more likely to be seismic -- in the right
> frequency range and such a wave would
> increase in amplitude as it passed a spot. It would
> never be noticed by a person.
>
> I think the Canary Islands wiggled...
>
>
> Sterling K. Webb
> ------------------------------------------------------------------------------
>
> ----- Original Message ----- From: "Matson, Robert D."
> <ROBERT.D.MATSON at saic.com>
> To: <meteorite-list at meteoritecentral.com>
> Sent: Wednesday, June 02, 2010 5:47 PM
> Subject: Re: [meteorite-list] A Twisted Meteor Trail Over Tenerife
>
>
>> 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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Received on Thu 03 Jun 2010 05:15:16 AM PDT