Out-of-focus find

While focusing a telescope on objects in deep space, researchers happened to collect images that enabled them to answer a question much closer to home: How wide are the glowing vapor trails known as meteors?

THAT’S HOT. The incandescent vapor trail of this meteor (out-of-focus diagonal line from lower left to upper right) was probably no more than about 1 centimeter wide. Iye, et al.

When extraterrestrial objects blaze through Earth’s atmosphere, they typically start to glow at heights of about 100 kilometers. Telescopes that observe deep-space phenomena are focused at infinity, so any meteor that shows up in images is far out of focus, says Masanori Iye, an astronomer at the National Observatory of Japan in Tokyo. Previous research had suggested that these incandescent trails are less than 1 meter wide, but the images didn’t allow further precision, he notes.

Some of the images that Iye and his colleagues made while observing the Andromeda galaxy in August 2004 also captured the ghostly streaks of meteors. To infer their true width, the researchers first estimated how many photons the telescope detected at a particular wavelength, radiated by oxygen atoms after high-energy collisions. Then they could estimate the number of such photons that the meteor had radiated in all directions, says Iye. Finally, knowing the density of oxygen atoms at an altitude of 100 km, the researchers could estimate the width of a vapor trail.

The brightness of a meteor provides a good idea of the size of particle creating it. For an object about the size of a sand grain, the researchers estimate that the resulting trail measured just over 1 centimeter wide. On average, each vapor trail that they analyzed was about 10 times as wide as the object that had vaporized to create it. The researchers report their findings in the Aug. 25 Publications of the Astronomical Society of Japan.

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