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)

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)

Crew in Britain's first ever full-size reconstructed sea-going Bronze Age boat, paddle out to sea near to the National Maritime Museum as it makes its maiden voyage on March 6, 2013 in Falmouth, England. (Photo by Matt Cardy)

Dachshunds are seen during a performance and art installation titled “Dachshund U.N.” at the Melbourne Museum on May 15, 2010 in Melbourne, Australia. The installation by Perth artist Bennett Miller is part of the New Wave Festival and sees 47 dachshunds representing national delegates taking part in a meeting of the United Nations' Commission on Human Rights, examining the role of the United Nations as a risk management organisation. (Photo by Lucas Dawson/Getty Images)

Stuart Craig of Washington tries out a Sig Sauer 1911 model Scorpion pistol at the Sig Sauer booth at the National Shooting Sports Foundation's 34th annual Shooting, Hunting, Outdoor Trade (SHOT) Show at the Sands Expo and Convention Center January 17, 2012 in Las Vegas, Nevada. The SHOT Show is the largest annual gathering of shooting professionals with more than 1,600 exhibitors and 30,000 attendees expected. (Photo by Ethan Miller/Getty Images)

“Kilauea Rules”. The most extreme place we put ours kayakers to paddle till now. Photo location: Big Island, Hawaii. (Photo and caption by Alexandre Socci/National Geographic Photo Contest)

“DC3 Wreck”. A capture of a US military DC3 plane wreck at the southern black beach in Iceland. Photo location: Iceland. (Photo and caption by Naian Feng/National Geographic Photo Contest)

This 1972 VW Beetle was one of over 150 cars at the eighth annual historic U.S Route 40 Mini-Nationals car show held on Sunday at Tecumseh high school. (Photo by Marshall Gorby/AP Photo)