Workers demonstrate outside the factory of Hua Yang Printing Holdings Co Ltd on October 30, 2007 in Shenzhen of Guangdong Province, China. Over 1,000 workers of the company have blocked the 107 State Highway where the firm is located, to protest against their employer, who owed half a month's salary to the workers. (Photo by China Photos/Getty Images)

“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)

Female Chimpanzee “Fifi” eats carrots as she sits in her enclosure at Taronga Zoo on her 60th birthday May 21, 2007 in Sydney, Australia. Fifi is the oldest of the Zoo's chimp population, which consists of 19 individuals. (Photo by Ian Waldie/Getty Images)

Flames quickly grow as firefighters set a backfire on the eastern front of the Park Fire, which has grown to 360,141 acres and is 12 percent contained, on July 28, 2024 near Chico, California. Strong winds and dried vegetation fueled the fire that exploded 70,000 acres in the first 24 hours after a man allegedly pushed a burning car into a ravine to intentionally set the blaze. (Photo by David McNew/Getty Images)

Waverly Fire's Tell Hanes, left, and Southeast Fire's Trey Wayne, right, jump over freezing water to high five while participating in a Surface Ice rescue technician course on Friday, January 6, 2023, at Holmes Lake Park in Lincoln, Neb. The International Rescue and Relief department at Union college held rescue training course at Holmes Lake for students and local fire departments. (Photo by Kenneth Ferriera/Lincoln Journal Star via AP Photo)

A girl marches alongside Salvadoran soldiers during the parade commemorating Independence Day in San Salvador, El Salvador September 15, 2016. (Photo by Jose Cabezas/Reuters)

People look at huge waves crashing on the San Esteban de Pravia seafront, northern Spanish region of Asturias February 8, 2016. (Photo by Eloy Alonso/Reuters)

A police officer lies on the street after being run over by a bus during a protest against the increase in the price of public transport in San Cristobal, Venezuela March 29, 2016. (Photo by Carlos Eduardo Ramirez/Reuters)