“Contrails (short for “condensation trails”) or vapour trails are artificial clouds that are the visible trails of condensed water vapour made by the exhaust of aircraft engines. As the hot exhaust gases cool in the surrounding air they may precipitate a cloud of microscopic water droplets or, if the air is cold enough, tiny ice crystals”. – Wikipedia

Photo: An airplane leaves a vapor trail as it flies in front of he moon on January 17, 2007 above Hanover, Germany. (Photo by Alexander Hassenstein/Getty Images)

David Sharp, an engineer with Lockheed Martin, displays the “Samurai Flyer”, an aviation design inspired by the maple seed, during the Association for Unmanned Vehicle Systems International Conference August 16, 2011 in Washington, DC. Lockheed Martin unveiled the new design and demonstrated vertical takeoff and landing, stable hover, and on-board video streaming of the aircraft during their demonstration. (Photo by Win McNamee/Getty Images)

The public get the first view at the opening of the new miniature model Knuffingen Aiport at Miniatur Wunderland on the airport's opening day on May 4, 2011 in Hamburg, Germany. Miniatur Wunderland is the world's largest model railroad landscape, and the model airport, also the world’s largest, goes into operation following 6 years of development and construction and an investment of EUR 3.5 million. The airport is a reproduction of Hamburg’s international airport and includes 40 aircraft that take off and land and 90 vehicles that autonomously move around the runways on May 4, 2011 in Hamburg, Germany. (Photo by Stuart Franklin/Getty Images)

A Felix Airways plane is seen after it was destroyed by an airstrike at the international airport of Yemen's capital Sanaa, April 29, 2015. Jets from a Saudi-led alliance destroyed the runway of Yemen's Sanaa airport on Tuesday to prevent an Iranian plane from landing there, Saudi Arabia said, as fighting across the country killed at least 30 people. Airport officials said the strikes set a civilian aircraft operated by Yemeni Felix Airways ablaze. (Photo by Khaled Abdullah/Reuters)

The zombies, cowgirls, and witches were out in force Saturday night on Clematis Street as thousands of people came to Moonfest to celebrate Halloween. They came from Broward County, Boynton Beach, Wellington, Port St. Lucie, and as far away as Germany and Sweden. Photo: Joe Smith, 60, Boca Raton. (Photo by Thomas Cordy/The Palm Beach Post)

Rescuers work at the traffic accident site on April 1, 2011 in Xi'an, Shaanxi province of China. A truck collided with a bus at a cross on Friday morning. As the truck headed for the sidewalk, it collided into a pedestrian and 6 vehicles which were stopped nearby. As a result 16 people were injuried, one currently has severe injuries. (Photo by ChinaFotoPress/Getty Images)

Brush and trees are engulfed in flames after firefighters set a backburn along Highway 191 in an attempt to control a raging wildfire on June 10, 2011 in Nutrioso, Arizona. The fire, which is five percent contained, has so far consumed over 400,000 acres of land and destroyed 29 homes. (Photo by Kevork Djansezian/Getty Images)