Full length portrait of female skier, Sierra Nevada Mountains in California, USA. (Photo by Anatoliy Gleb/Getty Images)

Medic James E. Callahan of Pittsfield, Mass., gives mouth-to-mouth resuscitation to a dying soldier in war zone D, about 50 miles northeast of Saigon, June 17, 1967. Thirty-one men of the 1st Infantry Division were reported killed in the guerrilla ambush, with more than 100 wounded. (Photo by Henri Huet/AP Photo)

Children of the Roma community play as they cool off in a fountain in the main square of Pristina, Kosovo on June 14, 2017. (Photo by Armend Nimani/AFP Photo)

Public Space series, 2015. This series by Morteza Niknahad and Behnam Zakeri tends toward cinema, taking an almost cartoonish view of modern life in Iran. This work was inspired by the social life of dolphins. (Photo by Morteza Niknahad and Behnam Zakeri/The Guardian)

A general view shows smoke and volcanic ashes billowing from volcano Cotopaxi in Pedregal, Ecuador, late 07 October 2015. (Photo by Jose Jacome/EPA)

This photo taken November 10, 2015 shows homeless street children sleeping in a park in Manila. The Philippines has swept 20,000 homeless from the streets, cancelled hundreds of flights and declared public holidays in Manila to ensure a safe and efficient summit of 21 world leaders next week, officials say. (Photo by Jay Directo/AFP Photo)

Lightning strikes near Jacobsdorf at the Oder-Spree district in eastern Germany, September 1, 2015. (Photo by Patrick Pleul/AFP Photo)

An airplane crosses a nearly full-moon on its way to Los Angeles International Airport near Whittier, Calif., Thursday, December 24, 2015. Not since 1977 has a full moon dawned in the skies on Christmas. (Photo by Nick Ut/AP Photo)