A picturesque supercell formation in the northwest of Booker, Texas from June 2013. (Photo by Mike Olbinski/Barcroft Media)

Senator Barack Obama (D-IL) (R) stands in front of Senator Hillary Clinton (D-NY) as they arrive for U.S. President George W. Bush's annual State of the Union speech to a joint session of Congress at the U.S. Capitol in Washington in this January 23, 2007 file photo. Hillary Clinton announced her second run for the presidency on April 12, 2015 starting her campaign as the Democrats' best hope of fending off a crowded field of lesser-known Republican rivals and retaining the White House. (Photo by Larry Downing/Reuters)

A girl uses her mobile phone during the evening at the National Park in Khartoum, Sudan, April 24, 2015. (Photo by Mohamed Nureldin Abdallah/Reuters)

The space shuttle Endeavour is transported to the California Science Center in Exposition Park from Los Angeles International Airport (LAX) in Los Angeles, California. (Photo by Kevork Djansezian)

The world's biggest wild animal farmer, Carr Hartley of Rumuruti in Kenya, sells animals to zoos, circuses and film companies. (Photo by Maxim Ruston/BIPs/Getty Images). November 1956

A runner in fancy dress participates in the Virgin London Marathon 2013 on April 21, 2013 in London, England. (Photo by Tom Dulat/Getty Images)

A man walks on a bridge crossing over the Besor stream on a rainy day, near Kibbutz Tze'elim in Israel's southern Negev desert February 16, 2017. (Photo by Amir Cohen/Reuters)

Colombian-Spanish actress Juana Acosta attends the Fotogramas Awards 2012 at Joy Eslava Club on March 12, 2012 in Madrid, Spain. (Photo by Carlos Alvarez/Getty Images)