On the second straight day of record-setting temperatures, Maddy Hacker is hoisted up by friend Jasmine Harper, both of McLean, Virgnia, as they attempt an acrobatic stunt in front of the U.S. Capitol in Washington, U.S., February 21, 2018. (Photo by Kevin Lamarque/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)

Members of the SubCielo company perform during the fifth annual Puerto Rico Circo Fest in San Juan, Puerto Rico, Saturday, March 10, 2018. The festival is held simultaneously in several spots on the streets of the Old San Juan city on March 10–11. (Photo by Ricardo Arduengo/AFP 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)

Indian artists dress up as the Hindu deity “Hanuman” – the monkey God in Hindu mythology – to mark the Rama Navami festival in Bangalore on March 25, 2018. Rama Navami is a spring Hindu festival that celebrates the birthday of the deity Rama. He is particularly important to the Vaishnavism tradition of Hinduism, as the seventh avatar of Vishnu. (Photo by Manjunath Kiran/AFP Photo)

South Vietnamese forces escort suspected Viet Cong officer Nguyen Van Lem (also known as Bay Lop) on a Saigon street February 1, 1968, early in the Tet Offensive. Moments later, Lem was executed by Gen. Nguyen Ngoc Loan, chief of the national police. (Photo by Eddie Adams/AP Photo)

An employe of Russian Space Training Center hangs out to dry space suits of Russian cosmonaut Anatoly Ivanishin, NASA's U.S. flight engineer Kathleen Rubins, and Japanese space agency's flight engineer Takuya Onishi, right, after their undergoing training near in Noginsk, 60 km (38 miles) east of Moscow, Russia, Wednesday, July 2, 2014. The training was intended to simulate the capsule landing on water. Russian cosmonaut Anatoly Ivanishin, Japanese space agency's flight engineer Takuya Onishi, and NASA's U.S. flight engineer Kathleen Rubins are being trained for a future mission to the International Space Station. (Photo by Alexander Zemlianichenko/AP Photo)

North Koreans wave flower bouquets and balloons as they march during a parade at the Kim Il Sung Square on Tuesday, May 10, 2016, in Pyongyang, North Korea. (Photo by Wong Maye-E/AP Photo)