A view of the spectacular colour of clouds at sunset on January 17, 2005 in Beijing, China. (Photo by China Photos/Getty Images)

Amundsen-Scott South Pole Station experiences months of darkness. The sun dips below the horizon on March 21, after which follows several weeks of twilight before complete darkness results. Photo taken on June 25, 2009. (National Science Foundation/Jeremy Johnson)

Chinese butchers catch a pig to slaughter on January 31, 2005 in Jinzhai County, Anhui Province, China. (Photo by Cancan Chu/GettyImages)

An ice swimming enthusiast dressed as Neptune takes to the frigid waters of Orankesee lake during the 27th annual "Winter Swimming in Berlin" on January 8, 2011 in Berlin, Germany. A local swimmers' group called the “Berlin Seals” invite ice swimmers from across Germany and abroad to the annual event. Members claim ice swimming is good for the body's blood circulation. (Photo by Sean Gallup)

The Dora the Explorer balloon moves through Times Square during the Macy's Thanksgiving Day parade Thursday, November 23, 2006 in New York. (Photo by Frank Franklin II/AP Photo)

An enterprising Chinese man pulls a bicycle cart packed high with bags of recyclable plastic containers in Shanghai July 25, 2002. The man sells each kilogram (2.2 pounds) of plastic for 0.08 yuan ($.01) to a nearby depot. (Photo by Claro Cortes IV/Reuters)

In this May 4, 2014 photo, a miner holds an amalgam of mercury and gold he mined after working a 28-hour shift at an illegal gold mining process, in La Pampa, in Peru's Madre de Dios region. Thousands of artisanal gold miners sweat through the long shifts and endure, for a few grams of gold, the perils of collapsing earth, limb-crushing machinery and the toxic mercury used to bind gold flecks. (Photo by Rodrigo Abd/AP Photo)

A man jokingly poses with a new installation of British graffiti artist Banksy's art in New York, October 20, 2013. (Photo by Carlo Allegri/Reuters)