Wedges of an orange generate enough current and electrical juice – 3.5 volts – to power an LED. The fruit’s citric acid helps electrons flow from galvanized nails to copper wire in this 14-hour exposure. This image was published in September’s Visions of Earth, a trio of photos that appear in each issue of National Geographic. (Photo by Caleb Charland/National Geographic)

Actors wearing masks of Syrian President Bashar al-Assad and Russian Prime Minister Vladimir Putin perform with body bags during a demonstration outside United Nations headquarters on January 24, 2011 in New York City. Protesters called on the U.N. Security Council to pass a resolution to attempt to halt al-Assad's crackdown on the Syrian uprising. (Photo by Mario Tama/Getty Images)

Dr. Christopher Brown (R), the Director of the Ashmolean, talks with Colin Harrison, the Ashmolean's Senior Curator of European Art, in front of a painting by Edouard Manet entitled “Portrait of Mademoiselle Claus” from 1868 in the Ashmolean Museum on February 24, 2012 in Oxford, England. The painting has been sold to a foreign buyer for 28.35 million GBP, however the Government has extended a temporary export bar on the artwork until August to give the Ashmolean an opportunity to raise funds to retain the painting in the UK. (Photo by Oli Scarff/Getty Images)

Katie Francis, a member of the Difficult Access Team from Wiss, Janney, Elstner Associates, inspects a gargoyle while rapelling down one of the north tower on the west front of the National Cathedral while looking for damage from August's magnitude 5.8 earthquake and high winds from Hurricane Irene October 17, 2011 in Washington, DC. DAT members used cameras, cell phones and iPad computers to record places on the cathedral's west front where damage was apparent. (Photo by Chip Somodevilla/Getty Images)

Dancers of the English National Ballet perform The Nutcracker at the Coliseum on December 14, 2011 in London, England. (Photo by Ian Gavan/Getty Images)

Private Wallace Tratford arrives home on leave, Drouin, Victoria, ca. 1944. A.I.F. Private Wallace Tratford, son of 1st Constable James Tratford, Drouin's only policeman (responsible for area of 105 square miles; 3,000 people), arrives home on his first leave from New Guinea battlefronts since he was married.

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)

An iguana in Bali helped Julij Kopilović, age eight, from Slovenia, earn second runner-up in Amazing Animals. (Photo by Julij Kopilović/National Geographic)