This is a citation of an outside article. Gravyday is not responsible for its content. Original URL below. Why do aircraft leave contrails in the sky? These wispy man-made clouds have fascinated humans for a century, but what actually are they? IIn 1915, around 12 years after the world's first controlled powered flight, Austrian physicist Robert Ettenreich was watching an aircraft skirting across the sky in Southern Tirol when he noticed something – a long wispy cloud trailing out behind it.(more)
