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)

Members of the Al-Baraa bin Malek batallion, part of the Free Syria Army's Al-Fatah brigade, duck to the ground as they pull a man (R) who was shot by a sniper twice in the Bustan al-Basha district of the northern city of Aleppo on October 20, 2012. (Photo by Javier Manzano/AFP Photo)

In this January 12, 2015 photo, a wall of collectable sneakers are displayed at Sneaker Pawn in the Harlem section of New York. Basketball sneakers can re-sell for hundreds of dollars, depending on the model, the size of the production run and how easy it is to find a pair in good condition. (Photo by Seth Wenig/AP Photo)

Mystical Forest. Tracey Jennings photographed this seven-gill shark in a kelp forest just off the shore of Simon's Town near Cape Town, South Africa. You don't need to travel far from cities to visit Narnia. This 7 gill shark was photographed in a kelp forest just off the shore of Simonstown near Cape Town, South Africa. (Photo by Tracey Jennings/National Geographic Travel Photographer of the Year Contest)

A Japanese twenty-year-old woman enjoys a cigarette during the annual Coming-of-Age Day ceremony at Toshimaen Amusement Park on January 11, 2010 in Tokyo, Japan. 1.27 million young people celebrate their passage into adulthood on the day while they become eligible to drink alcohol, smoke and vote at the age of 20. (Photo by Koichi Kamoshida/Getty Images)

Fireworks light up the London skyline and Big Ben just after midnight on January 1, 2012 in London, England. Thousands of people lined the banks of the River Thames in central London to see in the New Year with a spectacular fireworks display. (Photo by Peter Macdiarmid/Getty Images)

Crowds Gather For New Year's Ball Drop In Times Square on December 31, 2011 in New York City. (Photo by Michael Loccisano/Getty Images)

Mira Saville, 11, spins in her petticoat on the sand at the Nashuva Spiritual Community Jewish New Year celebration on Venice Beach in Los Angeles, California, United States September 14, 2015. As Jews take part in the Tashlich prayer, a Rosh Hashanah ritual, bread crumbs are tossed into the waters to symbolically cast away sins. (Photo by Lucy Nicholson/Reuters)