A walruses at Hagenbeck Zoo in Hamburg, Germany on July, 7, 2015. (Photo by Werner Struss/Startraks action)

An airplane passes the moon as it makes its approach to Philadelphia International Airport, Sunday, September 7, 2014, in Philadelphia. (Photo by Matt Rourke/AP Photo)

The Yakutat Glacier is seen during a flight over southeastern Alaska near the town of Yakutat, October 7, 2014. (Photo by Bob Strong/Reuters)

A competitor walks on tightrope during a performance in Taizhou, Zhejiang Province, China, May 7, 2016. (Photo by Reuters/China Daily)

A keeper stands next to llamas during the Annual Stocktake at ZSL London Zoo in London, Britain February 7, 2018. (Photo by Tom Jacobs/Reuters)

A cadet lies on the grass after collapsing during a promotion ceremony at a police school in Bogota December 7, 2012. (Photo by John Vizcaino/Reuters)

An Afghan National Army (ANA) soldier assigned to the Mobile Strike Force Kandak fires a RPG-7 rocket-propelled grenade launcher during a live-fire exercise supervised by the Marines with the Mobile Strike Force Advisor Team on Camp Shorabak, Helmand province, Afghanistan, May 20, 2013. The Marines with the Mobile Strike Force Advisor Team instructed and mentored their ANA counterparts on how to properly utilize their weapons systems. (Photo by SSgt Ezekiel R. Kitandwe/RCT 7)

People walk under stands with balloons placed along the former Berlin Wall location at Mauerpark, which will be used in the installation “Lichtgrenze” (Border of Light) in Berlin November 7, 2014. A part of the inner city of Berlin will be temporarily divided from November 7 to 9, with a light installation featuring 8000 luminous white balloons to commemorate the 25th anniversary of the fall of the Berlin Wall. (Photo by Pawel Kopczynski/Reuters)