“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)

A polar bear fast asleep at London Zoo. (Photo by Fox Photos/Getty Images). 1961

Impala pictured in the Kruger National Park on December 7, 2007 in Mpumalanga, South Africa. (Photo by Warren Little/Getty Images)

A female hippopotamus named “Mali”, which means Jasmine, eats fruits arranged to look like a cake during her 50th birthday celebration at Dusit Zoo in Bangkok, Thailand September 23, 2016. (Photo by Chaiwat Subprasom/Reuters)

Thailand's King Bhumibol Adulyadej in serious portrait January 01, 1960. Thailand's Royal Palace said on Thursday, October 13, 2016, that Thailand's King Bhumibol Adulyadej, the world's longest-reigning monarch, has died at age 88. (Photo by John Dominis/The LIFE Picture Collection/Getty Images)

Umbrellas are placed over the statute of the Beatles, during a photocall, on Liverpool's waterfront, in Liverpool, England, Wednesday, March 22, 2017. The city of Liverpool is getting set to celebrate the half-centenary of “Sgt. Pepper's Lonely Hearts Club Band”, one of the most influential albums by local heroes The Beatles. (Photo by Peter Byrne/PA Wire via AP Photo)

Members of a propaganda troupe perform in a public square in Pyongyang on April 12, 2017. (Photo by Ed Jones/AFP Photo)

A hostess sits at a restaurant with paintings depicting Thailand's King Bhumibol Adulyadej hanging on a wall in Bangkok, Thailand, June 6, 2016. (Photo by Athit Perawongmetha/Reuters)