A murmuration of migrating starlings is seen across the sky in southern Israel December 31, 2015. (Photo by Amir Cohen/Reuters)

The moon rises behind the skyline and financial district in Toronto, November 25, 2015. (Photo by Mark Blinch/Reuters)

A child parades on a float during the Bun Festival on May 25, 2015 in Hong Kong, Hong Kong. One of Hong Kong's most colourful cultural celebration event, Cheung Chau Bun Festival, will be staged on 25 May 2015 (Monday) till 26 May 2015 midnight (Tuesday). This festival has over 100 years of history. Every year, thousands of people descend upon the tiny island for The Piu Sik (Floating Colours) Parade, Lucky Bun (Ping On Bun) and The Bun Scrambling Competition, the ancient custom during the festival. (Photo by Lam Yik Fei/Getty Images)

This photo taken on December 2, 2015 shows a lenticular cloud forming as white streaks from airplanes mark the blue sky, in a rare atmospheric phenomena above the town of Gevgelija on December 2, 2015. Lenticular clouds have been regularly confused for UFOs throughout history due to the their smooth, round or oval lens-shaped structure. (Photo by Armend Nimani/AFP Photo)

Brandy Shelton of Greensboro, North Carolina, “twerks” for a group of bikers on Ocean Boulevard during the 2015 Atlantic Beach Memorial Day BikeFest in Myrtle Beach, South Carolina May 22, 2015. After three people were killed and seven wounded in shootings during 2014 Bikefest, State officials called for an end to the event that draws thousands to the family-friendly beach town.Their efforts were unsuccessful. Bikers returned to Myrtle Beach – just a week after a bloody motorcycle gang shootout in Waco, Texas. But this time authorities are more prepared, with dozens of new surveillance cameras and a police force three times the size of last year's. (Photo by Randall Hill/Reuters)

Relatives and friends react during the funeral of Bryan Sandoval, 17, a victim of a landslide that has left at least 112 dead and 350 missing people, in El Cambray II village, Santa Catarina Pinula, Guatemala, 04 October 2015. The landslide took place on 01 October 2015 when heavy rains saturated the soil. (Photo by Esteban Biba/EPA)

Ukrainian Air Force officers attend a graduation ceremony at the National University of Defence of Ukraine in Kiev, April 24, 2015. (Photo by Gleb Garanich/Reuters)

A competitor participates in the Tough Mudder challenge near Henley-on-Thames in southern England May 2, 2015. (Photo by Eddie Keogh/Reuters)