Trail in the sky

I took this picture in the school. One of the students asked me about the line across the sky. It was actually caused by a jet which just passed by. Like cars, jets have exhaust, which is the gas or vapor that is created when an engine burns fuel. When the exhaust escapes from a jet engine, it leaves a trail in the sky. It is freezing cold very high in the sky and the stripes the jets leave behind are ice crystals and cooled water. The water droplets and ice crystals are very light, so they can actually float in the sky! They are also called “vapor trail” or “contrail.”