Pictured here are three contrails intersecting that create non-congruent alternate interior angles. The two thicker contrails on the outside are cut by a transversal contrail, and this always makes interior angles, but since the two outer lines are not parallel I also know that the interior angles are not congruent. Contrails are created from the exhaust from jets and planes cutting through the air. Ever since planes started becoming more commercial about half a century ago, contrails have been seen all over the sky. On a clear, blue-skied day, contrails can always be seen above dicing up the clean blue sky. Contrails are not so much used as they are just seen and noticed on an everyday basis. In my life I dont believe I have ever seen a perfectly blue sky without contrails cutting through it. Contrails are created by thousands of pilots everyday and seen by millions and probably billions of people on the ground everyday.
I found this image online at this address: http://astrobob.areavoices.com/tag/contrail/