Aviation has fascinated and mystified people ever since the Wright brothers first took flight more than one hundred years ago. When you look up to the sky, you may notice that planes leave behind white streaks that often linger for some time. What exactly causes these streaks?
Airplane vapor trails
Airplane vapor trails, more commonly known as contrails, form when airplane exhaust and cold air combine. As airplanes burn fuel, they produce exhaust, causing gases, water vapor and solid particles to flow out of the engine. When these substances meet with the low air temperatures found at cruising altitude, the vapor freezes around the particles, producing white cloud-like patterns behind the plane. Contrails formed in dryer air tend to disappear almost as soon as they appear. Humid air can create persistent contrails which remain in the sky for longer lengths of time, either in thin straight lines or as spreading shapes that appear more like natural clouds.