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)

Bangladeshi fisherman feed their otters as they catch fish in Narail some 208 kms from Dhaka on March 11, 2014. The fishermen are using a rare technique that relies on coordination between man and trained otters, a centuries-old fishing partnership that has already long died out in other parts of Asia. (Photo by Munir Uz Zaman/AFP Photo)

A bull savar (jockey) guides his bulls as he competes in a bull race on the outskirts of Islamabad, Pakistan July 1, 2018. (Photo by Faisal Mahmood/Reuters)

World War Two veteran Abla Begaliyev, 91, is seen in an undated handout picture (L), poses for a picture in Arashan (Top R) and at home in Kyrgyzstan April 14, 2015. Begaliyev served in the border guard cavalry from February 1942 until April 1947. Originally from Kyrgyzstan, he fought on the Ukrainian front and relocated to the border with Afghanistan at the end of World War Two. As the world marks the 70th anniversary of the end of World War Two, Reuters photographers the length and breadth of the former Soviet republics (CCCP) captured portraits of Red Army veterans, mostly now in their 80s and 90s, today and through archive pictures at the time. More than 20 million Soviet citizens were killed in the war. (Photo by Vladimir Pirogov/Reuters/Family handout (L))

Aenne Schwarz as a “daughter” and Anna Sophie Krenn on Thursday, September 8, 2017, during the photoprobe of “Paradies flood / Lost symphony / Part one of the klimatrilogie” in the Akademietheater in Vienna, Austria. The piece premiered on September 9, 2017. (Photo by Georg Hochmuth/APA)

People dance Tuesday, April 28, 2015, in Baltimore. Maryland's governor vowed there would be no repeat of the looting, arson and vandalism that erupted Monday in some of the city's poorest neighborhoods. (Photo by Matt Rourke/AP Photo)

Small transportation boats, known as bumboats, leave trails of light as they travel across Marina Bay past the skyline of Singapore in this photo taken in 2004. Singapore holds a Jubilee weekend from 7 to 10 August to celebrate the 50th anniversary of its independence. Fifty years ago, hundreds of small boats lined the Singapore river in the city centre. Today, most small boats are gone, except a handful of neon-lit tourist ferries. Maritime trade is still the backbone of the city-state but after decades of rapid growth Singapore, which at less than half the size of London is among the world’s most densely populated nations, is also a popular tourist destination and a thriving global financial hub. (Photo by Edgar Su/Reuters)