19. They help predict the weather

You probably already know this, but just in case, did you know that the contrails or the tracks that are left by planes are actually made of water vapor? These can actually help in weather prediction.

When thin lines disappear soon, it shows that the weather is more stable with low humidity. When they are thick and last longer, it means a storm is likely to come.  So tell a friend about this so that they also know.