[meteorite-list] A Twisted Meteor Trail Over Tenerife

From: Matson, Robert D. <ROBERT.D.MATSON_at_meteoritecentral.com>
Date: Wed, 2 Jun 2010 15:47:56 -0700
Message-ID: <7C640E28081AEE4B952F008D1E913F170396CDD2_at_0461-its-exmb04.us.saic.com>

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
Received on Wed 02 Jun 2010 06:47:56 PM PDT