North Korean children wave to people on a Chinese tourist boat on the banks of Yalu River near the Chongsong county of North Korea, opposite the Chinese border city of Dandong, May 8, 2011. (Photo by Jacky Chen/Reuters)

A riot policeman uses a baton to hit a rioting University of Nairobi student in Kenya's capital Nairobi, in this May 20, 2014 file photo. (Photo by Noor Khamis/Reuters)

A protestor performs outside the parliament during a demonstration against austerity measures announced by the Spanish government in Madrid, Spain on September 29, 2012. (Photo by Andres Kudacki/Associated Press)

Yuri Gagarin does not always show up in full-scale astronautics. In this picture he smiles during his summer vacation in Sochi, Russia in 1961 with sunglasses and sunhat in the camera. (Photo by Imago/Eastnews)

An OV-10 Bronco aircraft, decorated with World War One commemoration motifs, flies over Flanders international airport, ahead of the world's first Short Take Off & Landing competition on sand, in Wevelgem, Belgium May 8, 2018. (Photo by Francois Lenoir/Reuters)

A family wearing traditional Japanese clothing posed for a photograph during spring season in one of the garden in Kiyomizu dera, Kyoto prefecture, Japan on March 30, 2018. (Photo by Richard Atrero de Guzman/NurPhoto via Getty Images)

Angel Hall, 22, (C) and Bri Artis, 21, (R) dance in a silent disco on the fourth and final day of the Firefly Music Festival in Dover, Delaware on June 17, 2018. (Photo by Mark Makela/Reuters)

Prince Philip, Duke of Edinburgh practicing his bicycle polo technique, Windsor Great Park, Berkshire, 1964. (Photo by Norman Potter/Daily Express/Hulton Archive/Getty Images)