“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)

Contestant Emilce Lezcano, center, prepares for the evening gown portion of the “Miss Gordita” beauty contest in Asuncion, Paraguay, Saturday, April 25, 2015. In their elegant evening gowns and elaborate hair styles, the contestants defy the conventional idea that only skinny women can be beautiful. (Photo by Jorge Saenz/AP Photo)

Construction workers carry bricks on their heads near the country's parliament building in Naypyitaw November 11, 2014. Yangon lost its status as Myanmar's capital in 2005, after the former military junta carved a new seat of government from a parched wilderness some 380 km (236 miles) to the north and called it Naypyitaw (“Abode of Kings”). (Photo by Damir Sagolj/Reuters)

The CBRE Urban Photographer of the Year competition – now in its ninth year – encourages professional and amateur photographers to capture cities at work. Here: Dog Walker – 15:00. The competition allows photographers to enter up to 24 images, one representing each hour of the day. (Photo by Johanna Siegmann)

Graffiti is painted on the bathroom walls at a restaurant in the Williamsburg area of Brooklyn borough in New York, United States, October 1, 2015. Some 2.4 billion people around the world don't have access to decent sanitation and more than a billion are forced to defecate in the open, risking disease and other dangers, according to the United Nations. To mark World Toilet Day on November 19, Reuters photographers captured pictures of toilets in cities, towns and villages around the globe. (Photo by Shannon Stapleton/Reuters)

Somali security officers gather at the scene of a car bomb attack at the base for the African Union forces in Mogadishu, Somalia, 26 July 2016. Media reports say at least 10 people, including the security guards at the base which is located at Mogadishu's airport, have been killed after two car bombs exploded at the base. Somalia's Islamist militant group al-Shabab has claimed responsibility for the latest attack. (Photo by Said Yusuf Warsame/EPA)

In this November 28, 1966 file photo, one of the 10 beagles involved in the first test of the Veterans Administration Hospital in East Orange, N.J. smokes a cigarette through a machine linked to its windpipe by a plastic tube to test any link between smoking and emphysema. (Photo by AP Photo)

Four-man bicycle is powered by five chains and has brakes on both its wheels, 1948. The bike was built by Art Rothschild (top position) who broke three ribs while learning how to ride it. (Photo by Wallace Kirkland/Time & Life Pictures)