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The Corkscrew Meteor
startleman writes "Over on Space.com is an interesting image of a corkscrew meteor. 'On Jan. 1, 1986, [Jimmy Westlake] was photographing [Halley's comet] through his homemade 8-inch reflecting telescope..."About one minute into the exposure, I watched a meteor zip through the field of the telescope." When he developed the roll of slide film, he was astounded that '...Crossing the tail of Halley's comet was a corkscrew meteor trail with no fewer than 25 twists in it.' Westlake's photo was never published until today. He wonders if there are others out there."
But what do I know, IANAA(stronomer).
I forget what 8 was for.
Although I have never seen it in a photograph, couldn't this have been caused by visual waves caused by the atmosphere?
I believe that you may almost be on to something. IAAA (I Am An Astronomer) and the "visual waves" you speak of are called "seeing"--atmospheric turbulence tends to blur out the images of stars. Though stars are generally sized 1/1000 of an arcsecond (the largest is about 50/1000), the atmosphere blurs on a scale of a few arcseconds. So if the "corkscrew" were caused by seeing, one would expect the stars to be blurred by an amount similar to the amplitude of the "corkscrew", which we do see in the image.
However, seeing (turbulence) is random. The "corkscrew" is clearly not--it appears sinusoidal. A much more likely explaination is that the telescope mount is vibrating--this would cause sinusoidal smearing of all objects in the field. the meteor, which is moving, becomes a corkscrew; the stationary stars get smeared in the direction of the vibration (as is seen in the picture). The meteor appears about 1 minute into the "2 minute exposure", and has "25 corkscrews", so the vibration is at about a half a hertz. Thus it is likely that his mount wasn't quite sturdy enough for the 'scope, or winds were abnormally high that night. Alternatively, since he apparently accounts for sidereal motion (the telescope has electronic drives to track stars, compensating for the earth's rotation), maybe the drive motors have noise at half a hertz....
I think you are right. When I looked closer at the stars, they seemed motion blurred, but in an elliptical shape. This would happen if the telescope was vibrating back and forth, in one direction. Perhaps if the telescope was on the back of a pickup truck or something we would see this.
When you look at the wavy meteorite trail, it's not a perfect sine wave. It looks like it was "waving" on an axis that wasn't perpendicular to the direction of travel. In fact, the apparent direction of the waving seems to line up with the stars motion blur. It seems the axis of vibration is rotated twenty or thirty degrees counterclockwise from the direction of the meteor. Because the stars shape and the wave of the meteor are the same, I'm inclined to agree that this is some kind of vibrational anomoly.
What do you guys think?
The meteor appears about 1 minute into the exposure, but it doesn't take 1 minute for the meteor to cross the field of exposure, which is what you are implying by your "half a hertz" oscillation theory.
Now, the motors could have had a 60 hertz "hum" and the meteor was in the frame for just under half a second. That cycle rate is common for AC in North America, and I can belive a meteor streaking across the sky in half a second more than I can believe it streaked across the sky in a whole minute.
I've seen meteors do this, with naked-eye observations during one of the more active fall showers a few years ago. In fact, most of the larger or brighter ones seemed to do it with varying intensity. It's not atmospheric distortion. It's way too periodic.
I've also seen them with second or third order oscillations, making larger spirals like a big, fast, heavy leaf 'fluttering' to the ground.
I just assumed that it was the meteor tumbling like it's probably going to - considering it's not probably not an aerodynamically stable shape - and just spewing and sputtering ablating matter as it burned up.
Why is this a mystery? Anyone that's shot irregular flakes of rocks (or, say, pennies) out of a wrist-rocket or slingshot will see that they behave in much the same way - aerodynamically unstable objects tumbling and spinning from drag as they pass through the atmosphere at high speed.