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SYFY WIRE Bad Astronomy

A Puff of Celestial Smoke

By Phil Plait

The Earth is bombarded by cosmic debris on a daily basis. On average, about 100 tons of matter burns up in our atmosphere every day! Most of it consists of tiny particles no bigger than a grain of sand, but when they slam into our air at speeds of 50 kilometers per second or more, they get hot. This heat translates into light, and we see the flash of a meteor, commonly called a shooting star, across our sky.

Some of these can be very bright, and most leave a trail of material behind them (technically called a train). Sometimes, that train can glow for a long time, even several minutes.

My friend Babak Tafreshi caught just such a meteor with a persistent train when he was photographing the sky on Oct. 19, 2012 in northern Maine. He was able to make a short time-lapse video of it, too:

Note that the actual flash of the meteor is not in this shot, but the train is obvious. But what is it, really?

Iâve written about this before. What youâre seeing is not smoke, or burning particles. As a meteoroid (the actual solid chunk of material) blasts through the atmosphere, it violently compresses the air, heating it up hugely (note this isnât due to friction, but compression; like when a bicycle pump heats up

after as you use it). The heat is so intense it ionizes the gases, stripping electrons from their parent atoms. As the electrons slowly recombine with the atoms, they emit lightâthis is how neon signs glow, as well as giant star-forming nebulae in space.

The upper-level winds blowing that at that altitude (upwards of 100 km/60 miles above the Earthâs surface) create the twisting, fantastic shapes in the train. The actual details of how this works in meteor trains are not well understood, mainly because they are so difficult to spot and study. Itâs hard to point a telescope at a position in the sky when you donât know where or when a meteor will pass through.

In this case, you can see the familiar stars of the Big Dipper on the left, peeking in and out of the clouds. I actually wish the trainâs placement had been just a wee bit different: Then it would look like steam coming from the bowl of the Dipper!

Seeing a persistent train is rare. Iâve seen hundreds of meteors, maybe thousands, over the years but never, not once, have I seen a persistent train like that.

The only cure for that is to go out more and keep looking. Happily, thatâs something Iâm willing to do.

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