[meteorite-list] A Twisted Meteor Trail Over Tenerife

From: Sterling K. Webb <sterling_k_webb_at_meteoritecentral.com>
Date: Wed, 2 Jun 2010 18:40:23 -0500
Message-ID: <CD60C76B6DDD4FEC8BFE5D645C1115D0_at_ATARIENGINE2>

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 Wed 02 Jun 2010 07:40:23 PM PDT