A group of refugees walk on the railway tracks after crossing from Serbia, in Roszke, Hungary, Tuesday, Sept. 1, 2015 (AP)

A discarded stroller is left behind by refugees on the railway track on the border between Serbia and Hungary, in Roszke, Hungary, Tuesday, Sept. 1, 2015 (AP)

Kazakhstan's cosmonaut Aydyn Aimbetov (C), Russian cosmonaut Sergei Volkov and Denmark's astronaut Andreas Mogensen from the European Space Agency (top) wave as they board the Soyuz TMA-18M spacecraft at the Russian-leased Baikonur cosmodrome early 7 September 2, 2015. (Reuters)

Migrants walk on a field as they reach the village of Idomeni near the borders of Greece with Macedonia, September 2, 2015.(reuters)

Migrants fall as they rush to cross into Macedonia after Macedonian police allowed a small group of people to pass through a passageway, as they try to regulate the flow of migrants at the Macedonian-Greek border September 2, 2015 (Reuters)

photo provided by Compass Data/USGS, Blaine Horner of CompassData probes the snow pack at the highest point in North America along with setting up Global Position System equipment for precise summit elevation data on top of Denali in Denali National Park, Ak. The U.S. Geological Survey announced Wednesday, Sept. 2, 2015 (AP)

The Soyuz TMA-18M spacecraft carrying the crew of Aidyn Aimbetov of Kazakhstan, Sergei Volkov of Russia and Andreas Mogensen of Denmark blasts off from the launch pad at the Baikonur cosmodrome, Kazakhstan, September 2, 2015. (Reuters)

An overall view shows the Horseshoe Falls in Niagara Falls, Ontario, August 22, 2015. Picture taken August 22, 2015. (Reuters)

French soldiers and pilots work on Rafale jet fighters at the air base in Mont de Marsan, southwestern France, August 31, 2015. For decades a symbol of fruitless endeavours to sell French fighter jets abroad, the Mont-de-Marsan pilot training centre in southwestern France (Reuters)

A boy, sitting under a green transparent roof, is seen dressed in traditional attire while waiting to take part in a memorial rally dedicated to the people who were killed in the April 25 earthquake in Bhaktapur September 2, 2015 (Reuters)