When an airplane is flying in the sky, it creates a long strip of cloud behind. Condensation is mainly caused by the cooling and condensation of water vapor emitted by the aircraft or the wing disturbs the surrounding air causing the surrounding water vapor to condense into clouds. The appearance and duration of the condensing cloud determines by the atmospheric conditions at the altitude of the aircraft. If the atmosphere is dry, ice crystals will be quickly expelled. On the other hand if the humid air, it may last for a longer time and may transform into altocumulus or cirrocumulus.