A weeping South Vietnamese mother and her three children are shown on the deck of this amphibious command ship being plucked out of Saigon by U.S. Marine helicopters in Vietnam, April 29, 1975. (Photo by AP Photo)

Ultra orthodox children stick their tongues out as snow falls on March 2, 2012 in Jerusalem, Israel. This is the first time in four years that the Israeli captial has experienced snow fall. (Photo by Uriel Sinai/Getty Images)

A pro-democracy demonstrator fights with a Soviet soldier on top of a tank parked in front of the Russian Federation building on August 19, 1991, after a coup toppled Soviet President Mikhail Gorbachev. The same day, thousands in Moscow, Leningrad, and other cities answered Russian Republic President Boris Yeltsin's call to raise barricades against tanks and troops. (Dima Tanin/AFP/Getty Images)

Vietnamese military personnel in traditional dress take part in a parade celebrating the 40th anniversary of the end of the Vietnam War which is also remembered as the fall of Saigon, in Ho Chi Minh City, Vietnam, Thursday, April 30, 2015. (Photo by Dita Alangkara/AP Photo)

A reveler and a child street vendor pose for a photo during the Banda de Ipanema Carnival parade in Rio de Janeiro, Brazil, Saturday, January 31, 2015. Rio's over-the-top Carnival is the highlight of the year for many local residents. Hundreds of thousands of merrymakers are beginning to take to the streets in open-air “blocos” parties. (Photo by Silvia Izquierdo/AP Photo)

Visitors look at a tower exhibit of 429 different kinds of pumpkins and squash from all over the world at the Buschmann and Winkelmann pumpkin farm on October 9, 2011 in Beelitz, Germany. The farm, located in Brandenburg state near Berlin, harvests tens of thousands of pumpkins from approximately 40 different kinds between August and October and is known for its elaborate, theme-based pumpkin exhibits. (Photo by Sean Gallup/Getty Images)

Long-tailed mayflies (Palingenia longicauda) mate on the surface of the Tisza river near Tiszakurt, Hungary, June 14, 2016. Millions of these short-lived mayflies engage in a frantic rush to mate and reproduce before they perish in just a few hours during “Tiszaviragzas” or Tisza blooming season from late spring to early summer every year. (Photo by Laszlo Balogh/Reuters)

Santa Claus greets a child during a visit to residents of the slum of Petare in Caracas, Venezuela, December 11, 2016. (Photo by Ueslei Marcelino/Reuters)