A reveller of the Salgueiro samba school performs during the second night of Rio's Carnival at the Sambadrome in Rio de Janeiro, Brazil, on February 13, 2018. (Photo by Mauro Pimentel/AFP Photo)

A reveller from Salgueiro performs during the second night of the Carnival parade at the Sambadrome in Rio de Janeiro, Brazil on February 13, 2018. (Photo by Sergio Moraes/Reuters)

Soldier boys at Fort Dix, N.J., learn something about guns during their working hours, as they show their girlfriends at a camp dance, December 13, 1940. In front row, playing with the coin amusement gun, from left: Pvt. Tom D'Amato of West Orange; Rose Sinkewicz, behind gun site, of Trenton; Julia Ivans of Trenton, and Pvt. Vernon Landers of Kearney. Back row: Pvts. William Sargent and William Corlies of Philadelphia. (Photo by AP Photo)

British theoretical physicist Stephen Hawking, Cambridge University Professor and Fellow, circa 1985. Stephen Hawking, the brightest star in the firmament of science, whose insights shaped modern cosmology and inspired global audiences in the millions, has died aged 76. (Photo by Gemma Levine/Getty Images)

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)

Racegoers attend day one of The Randox Health Grand National Festival at Aintree Racecourse on April 12, 2018 in Liverpool, England. (Photo by News Group Newspapers Ltd)

Children in a Hong Kong refugee resettlement area watch as former Vice President Richard Nixon shows them his badminton service. Nixon visited Hong Kong, April 4, 1964, during his tour of countries in the Far East. (Photo by AP Photo)

In this April 13, 2018 photo, motorcycle taxi driver Ricardo Medina, 60, transports vegetable vender Rigoberto Herrera Mendez, left, and coconut vendor Osvaldo Ochoa in Campo Florido, east of Havana, Cuba. The three men expressed hope that new government leadership will improve things, saying the country cannot move backwards. “We survive life with our work”, said Medina. (Photo by Ramon Espinosa/AP Photo)