The Northern Lights glow green in a spectacular light show above a field of trees frozen solid with snow. (Photo by Jaak Sarv/Solent News & Photo Agency)

Performers line up during the closing ceremony of the 2014 Winter Olympics, Sunday, February 23, 2014, in Sochi, Russia. (Photo by Darron Cummings/AP Photo)

Western lowland gorilla Kijivu holds her newborn baby at the Prague Zoo in the Czech Republic. (Photo by Isifa/Getty Images)

Coloured X-ray of a barn owl. A physicist has used X-ray to create an extraordinary collection of artwork. Arie van't Riets pictures reveal birds, fish, monkeys and flowers in an incredible new light. The 66-year-old, from Bathmen in the Netherlands, began X-raying flowers as a means to teach radiographers and physicians how the machine worked. But after adding a bit of colour to the pictures, the retired medical physicist realised the potential for an exciting new collection of art. (Photo by Arie van't Riet/Barcroft Media)

A visitor takes a picture of a display bearing hand prints of war heroes from the War of Resistance against Japan, at Jianchuan Museum Cluster in Anren, Sichuan Province, China, May 13, 2016. Tucked away in southwestern China's Sichuan province, a private collector stands virtually alone in exhibiting relics from the 1966-1976 Cultural Revolution. Monday marks the 50th anniversary of the start of the political movement, with no official commemorations planned. Official records whitewash the details of both periods, but admit that Mao made major mistakes. (Photo by Kim Kyung-Hoon/Reuters)

A minaret, that was damaged during fighting between Islamic State jihadists and government forces, is seen in Ben Guerdane, near the Libyan border, Tunisia April 10, 2016. After a U.S. air strike killed a Tunisian jihadist commander in western Libya in late February, dozens of Islamic State fighters sneaked across the border into Tunisia and attacked an army barracks and police bases in the town of Ben Guerdane. (Photo by Zohra Bensemra/Reuters)

A fireman pulls a woman and her dog to shore, by a row of houseboats on the river Seine in Paris France, Wednesday June 1, 2016. The Seine River has overflowed embankments in Paris as floods hit or threaten cities and towns around France. (Photo by Jerome Delay/AP Photo)

This May 11, 2016 photo shows the backside of a bus decorated with a provocative mural, in Acapulco, Mexico. (Photo by Enric Marti/AP Photo)