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)

Ivan Shamyanok, 90, shaves in his house in the village of Tulgovichi, near the exclusion zone around the Chernobyl nuclear reactor, Belarus March 15, 2016. “My sister lived here with her husband. They decided to leave and soon enough they were in the ground ... They died from anxiety. I'm not anxious. I sing a little, take a turn in the yard, take things slowly like this and I live”, he said. (Photo by Vasily Fedosenko/Reuters)

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)

CANADA: Stanley Ferdinand filets large trout he caught in Great Bear Lake in Deline, Northwest Territories, Canada September 8, 2016. (Photo by Pat Kane/Reuters)

The Mount Bromo volcano erupts in the Bryce Canyon, Utah. (Photo by Reynold Dewantara/2016 National Geographic Travel Photographer of the Year Contest)

Green Bay Packers' Johnathan Calvin rides a bike to NFL football training camp on July 27, 2017, in Green Bay, Wis. (Photo by Morry Gash/AP Photo)