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)

Indian men stand around sword fish for sale at a harbour a harbour in Chennai on June 5, 2016, as fishermen return with their catch after a 45-day fishing ban on the east coast of India. Authorities in the southern Indian state of Tamil Nadu had imposed a 45-day ban on fishing by mechanised vessels to protect marine life, with only “country boats” operating within five nautical miles off the coast. (Photo by Arun Sankar/AFP Photo)

A physically challenged girl looks at her brother as she is kept in a basin to seek alms from people on the street in Kano, Nigeria December 30, 2015. The girl has suffered from her condition since birth. (Photo by Reuters/Stringer)

Women look on as Sauber's German driver Pascal Wehrlein steers his car during the second practice session at the Monaco street circuit on May 25, 2017 in Monaco, three days ahead of the Monaco Formula 1 Grand Prix. (Photo by Andrej Isakovic/AFP Photo)

A 12th century manuscript of The Old Testament sits in the Chained Library of Hereford Cathedral after it's annual spring clean on January 24, 2012 in Hereford, England. (Photo by Christopher Furlong/Getty Images)

A woman looks at a swimmer getting herself warm after the annual Christmas winter swimming competition in the Vltava river in Prague December 26, 2014. (Photo by David W. Cerny/Reuters)

A cake decorated as a scene from the children's story “Little Red Riding Hood” is displayed at the Cake and Bake show in London, Britain October 3, 2015. (Photo by Neil Hall/Reuters)

Flames quickly grow as firefighters set a backfire on the eastern front of the Park Fire, which has grown to 360,141 acres and is 12 percent contained, on July 28, 2024 near Chico, California. Strong winds and dried vegetation fueled the fire that exploded 70,000 acres in the first 24 hours after a man allegedly pushed a burning car into a ravine to intentionally set the blaze. (Photo by David McNew/Getty Images)