A contrail over southwest Virginia, 19 March 2012, captured by Eric T Gunther. Via http://en.wikipedia.org/wiki/File:Con_Trail_Virginia.JPG
Contrails are a type of narrow, long cloud that can be caused by aircraft travelling through the cold air at high altitudes. They are caused either by condensation of water vapor from the engine exhaust as it is ejected into the cold air, or by condensation of water vapor already in the air around pressure changes due to vortices formed as air passes over the aircraft’s wing. Next time you are in a plane, if you can see a wing have a look; you might be able to see narrow vortices forming over the wing. It’s quite a dramatic sight! Depending on the altitude and conditions, they can appear as a short smudge or as a long, thin cloud stretching far across the sky.
When they form in the early morning or late evening, contrails can be mistaken for meteors, especially when the light catches them and can make them appear orange or golden. To tell the difference, look at them as they form. Is its leading end moving at a speed an aircraft might be able to move at? If it is, it’s an aircraft contrail. Meteors are fast. Does the leading end have an intensely bright fireball whose brightness varies in intensity? Meteor; we at least hope that aircraft aren’t bright, flickering fireballs!
For Science! 
Reblogged this on Kelsey L. Reed.