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)

Nine year old girl Barsati reacts while walking on a tightrope in Mumbai on February 11, 2014. Barsati, and her younger brother Rajababu, (4) earn an average of around 2000 rupees (32 dollars) per day from pedestrians and tourists performing various acts on the tightrope near the city's iconic landmark Gateway of India. (Photo by Indranil Mukherjee/AFP Photo)

“The Tonight Show” host Jimmy Fallon, center, exits the water during the Chicago Polar Plunge, Sunday, March 2, 2014, in Chicago. Fallon joined Chicago Mayor Rahm Emanuel in the event. (Photo by Andrew A. Nelles/AP Photo)

A prototype battery-powered plane, called Greased Lightning or GL-10 is pictured flying at NASA's Langley Research Center in this undated handout photo obtained by Reuters May 1, 2015. The plane, which has 10 engines and can take off like a helicopter and fly efficiently like an aircraft, is currently in the design and testing phase. (Photo by Reuters/NASA)

The figure of an eight-year-old boy is seen inside a suitcase on a Spanish civil guard scanner screen at the border between Morocco and Spain's north african enclave Ceuta, Spain in this handout photo released May 8, 2015. A 19-year-old woman was arrested May 7, 2015 for the attempted smuggling of the boy, who was checked by medics and handed over to juvenile prosecutors office, according to authorities. (Photo by Reuters/Ministerio Del Interior)

A model presents a creation from the Blonds Fall 2020 collection during New York Fashion Week in the Manhattan borough of New York, U.S., February 9, 2020. (Photo by Caitlin Ochs/Reuters)

Lady Gaga performs at Radio 1's Big Weekend 2011 at Carlisle Airport on May 15, 2011 in Carlisle, England. (Photo by Dave Hogan/Getty Images)

“Two Brothers”. We found about 20 lions eating a buffalo. When the male leaved the group we anticipated him to take photos. It is 8AM, light is perfect and the position too. The lion stops and looks down from the hill, another lion is coming up, it stiffens, I think that will be a fight, i'm tense, the camera is OK, the shots previously made perfect. The two meet, looking directly into their eyes, they sniff, rub against their heads, the tension drops, they start walking with the same step as when they were puppies, they are two brothers. Photo location: Masai Mara, Kenya. (Photo and caption by Massimo Mei/National Geographic Photo Contest)