Television actress Catherine Fuller visits Trafalgar Square in London and feeds the famous pigeons. (Photo by Harry Kerr/BIPs/Getty Images). 26th June 1956

“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)

Three secondary schoolboys smoking an illicit cigarette in Hyde Park, London. (Photo by Evening Standard/Getty Images). May 1972

Mr. Grindell Matthews with his latest invention, the new photographic gun which is the latest development in sky signs. 1933. It can throw a beam of light 15 miles into the sky. (Photo by Fox Photos)

Seven month old Christine Joy shares her pram with two 5 week old Gunsure Golden Cherry's cocker spaniel pups from Gunsure Kennels in Ashford, Middlesex. 22nd May 1953. (Photo by Fred Morley/Fox Photos)

The aurora borealis, or the northern lights occur over Derwentwater, near Keswick, England, Thursday October 8, 2015. The northern lights are the result of collisions between gaseous particles in the Earth's atmosphere with charged particles released from the sun. (Photo by Owen Humphreys/PA Wire via AP Photo)

A giant storm cloud can be seen in the sky above swimmers near Mollymook Beach, south of Sydney, March 5, 2014. (Photo by David Gray/Reuters)