What does this line in the sky mean?

Yes, it happens when I take off with my jet pack. :P Honestly, I think they're caused by planes. Not sure which ones though.

by Vee

It's a vapor trail. We used to love seeing these when we were kids especially if you could see the jet at the head of the line. We would lay on our backs on the lawn and watch them get wider as the breeze dissipated them.

by Gayle Beveridge

It's a contrail. It's a long cloud made by the vapour left behind by an aeroplane.

http://en.wikipedia.org/wiki/Contrail

by Jennifer Muirhead

I thinks its when the jets have passed.

by Gia

Vortices from aircraft.

by donjo

I find vapour trails interesting. One day I saw one in the shape of an X so I took a photograph.

by Marie Vonow