spectrography works by analyzing the um...you know...spectrum?
that's light.
the light given off by something that is incandescent....(that means it's so hot that it glows)

vapor trails are tiny crystalized ice particles. They don't glow with their own light. They reflect sunlight.

(cough)

you're logical fallacy for today is 'false equivalency'...(compression indeed. aircraft work by the principle of aerodynamic lift...the type of engine they use is irrelevant...geez)