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)

Burundian refugees gather on the shores of Lake Tanganyika in Kagunga village in Kigoma region in western Tanzania with their belongings, as they wait for MV Liemba to transport them to Kigoma township, May 17, 2015. Burundi's embattled President Pierre Nkurunziza sacked his defense and foreign ministers on Monday, five days after surviving an attempted coup by generals opposed to his bid for a third term in office. (Photo by Thomas Mukoya/Reuters)

People rush an injured woman to a local hospital in Peshawar, Pakistan, Monday, October 26, 2015. A powerful 7.7-magnitude earthquake in northern Afghanistan rocked cities across South Asia. Strong tremors were felt in Kabul, New Delhi and Islamabad on Monday. In the Pakistani capital, walls swayed back and forth and people poured out of office buildings in a panic, reciting verses from the Quran. (Photo by Mohammad Sajjad/AP Photo)

Iraqis run for cover as they flee Mosul's Al-Tayaran neighbourhood on February 28, 2017, during an offensive by Iraqi forces to retake the area from Islamic State (IS) group fighters. Hundreds of civilians fled through the desert to escape fighting and privation in Mosul, joining thousands of others who left their homes as conditions worsen in the city's west. (Photo by Ahmad Al-Rubaye/AFP Photo)

Tajammu Al-Ezza brigade fighters react while firing a Grad shell towards forces of Syria's President Bashar Al-Assad stationed in Salhab village, Hama countryside, May 7, 2015. (Photo by Mohamad Bayoush/Reuters)

Children play at a makeshift camp for migrants and refugees at the Greek-Macedonian border near the village of Idomeni, Greece, March 29, 2016. (Photo by Marko Djurica/Reuters)

Azat Shajbyrov reacts with a baby falcon on his head in a village of Bokonbaevo, Issyk-Kul area (270 km from Bishkek), Kyrgyzstan, 22 June 2016, as he dreams of continuing a family tradition of golden eagle hunting. Eagle and falcon hunting is an old Kyrgyz tradition. With their birds, Kyrgyz berkutchy hunt in the mountains and participate in the hunting festival “Salburun”. (Photo by Igor Kovalenko/EPA)