Thursday, February 03, 2005

Meteor mystery

posted by Tom at 1:20 AM UTC

One of my morning rituals is to check out NASA's Astronomy Picture of the Day. Today's picture shows what appears to be a meteor which has left behind a mysterious spiraling streak of light.

My first reaction to seeing this was "Baloney!" Most meteors or shooting stars are tiny motes of dust which enter the upper atmosphere at high velocity. The glowing streak is the result of super heated air surrounding the speeding particle. It seemed implausible to me that a typical meteoroid could produce a complex sinusoidal corkscrew like that.

Investigating further, I found this article which contains a few key pieces of evidence. The photo was taken by Jimmy Westlake on January 1st, 1986 while he was imaging that year's visitation of Halley's Comet. With that info I could locate the part of the sky the meteor crossed by using my Starry Night sky simulation software. Below is Westlake's original image on the left. On the right is the same field of view as generated by software.

From this you can determine the size of the streak. It turns out to be about 1 arc minute in width, or 1/60th of a degree. Meteoroids typically impact the upper atmosphere at an altitude of 50 miles or more. Straining to remember my high school trigonometry, I did a quick calculation:

sine(1/60˚) x 50 miles = 77 feet

If the meteor is 50 miles high, the apparent width of the wobble is about 77 feet! How could a tiny speck of grit create a spiral so large?

What other explanation could there be? Atmospheric turbulence perhaps? My suspicion is that it wasn't the meteor that was wobbling, but Westlake's telescope was vibrating imperceptibly during the time lapse exposure.

Googling further I found an inconclusive Slashdot discussion on this same subject. One suggestion was that the motor that slews Westlake's homemade telescope has a 60hz hum that spoiled this time lapse photograph in such a curious manner. Hmm...

I hope Chet or any readers out there can share some insight on this. Is it baloney or not?