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Re: (meteorobs) Persistent Train
OK, here's a long one... but pretty neat to contemplate if you do read it! :)
Actually, Dave, you pointed up the source of your own confusion when you called
the persistent train "smoky". In fact there is no smoke involved in this glowing
"after-image" we see sitting in the path of a meteor after that meteor has
passed... Instead, the persistent train is a large column of AIR (i.e., from our
own upper atmosphere) which is glowing due to its irradiation (and the resulting
"recombination", for you physicists) by the passing meteoroid.
As many amateur astronomers know, many of the nebulae we see in the sky are
actually visible to us because they are reradiating ultraviolet light from an
intensely bright star: HII regions, planetary nebulae, supernova remnants and
Wolf-Rayet nebulae are all of this type of "emission nebula". (In effect, you
can think of the radiating star as a "black light", and the surrounding gases as
the equivalent of a white shirt, worn in the presence of the light! The shirt
appears to glow, because it takes the "black" ultraviolet light and reradiates
some of it in the visible area of the spectrum...)
The glowing meteor train is actually just this same effect in our atmosphere: in
place of the intense star (or the black light), though, is the intensely glowing
meteor head. This meteor head results when a meteoroid slams into the atmosphere
at a hefty 25,000 - 150,000 miles per hour: the resulting conversion of kinetic
energy to radiation by friction is energetic enough to irradiate a large column
of air (1000 feet sounds reasonable - it may be even larger!) with ultraviolet
light - causing it to glow. And of course, this all happens at the speed the
ultraviolet radiation travels, i.e., the speed of light...
You can actually SEE this column of glowing air form behind a passing trained
meteor, if you happen to catch one in a telescope: the sight is lovely!
Hope this helps rather than confusing everyone further, :)
Lew
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