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)

A Tibetan woman displays her Qing Dynasty family dress in Zhailong Village on April 24, 2005 in Danba County of Ganzi Tibetan Autonomous Prefecture, Sichuan Province, China. (Photo by China Photos/Getty Images)

The combination of Venezuela's sky-rocketing prices and chronic product shortages have left many struggling to put regular food on their tables and maintain a balanced diet. According to one recent study, 87 percent of Venezuelans say their income is now insufficient to purchase their food needs. Here: All the food available in the house of Antonia Torres and her family, is pictured at their home in Caracas, Venezuela April 22, 2016. (Photo by Carlos Garcia Rawlins/Reuters)

A woman carries a water pump to work on February 11, 2017 in Almolonga, Guatemala. The Mayan town in the western highlands district of Quetzaltenango has surged in prosperity in recent years with high-productivity vegetable farming, exporting much of its excess crops to neighborning El Salvador. (Photo by John Moore/Getty Images)

Hikaru Cho believes that we should challenge our imaginations to create new work using traditional tools, not fancy computers and software. (Photo by Jim Marks/PA Wire)

“Cassowaries are large, flightless birds related to emus and (more distantly) to ostriches, rheas, and kiwis”, writes Olivia Judson in the September issue of National Geographic magazine. How large? People-size: Adult males stand well over five foot five and top 110 pounds. Females are even taller, and can weigh more than 160 pounds. Dangerous when roused, they’re shy and peaceable when left alone. But even birds this big and tough are prey to habitat loss. The dense New Guinea and Australia rain forests where they live have dwindled. Today cassowaries might number 1,500 to 2,000. And because they help shape those same forests – by moving seeds from one place to another – “if they vanish”, Judson writes, “the structure of the forest would gradually change” too. (Photo by Christian Ziegler/National Geographic)

Chinese woman Duo Zirong feeds stray cats at her home February 14, 2006 in Shanghai, China. Duo Zirong, a Daur ethnic minority group woman from Inner Mongolia and reported as the “Cat Woman”, has housed about 300 cats with her Shanghainese husband Liu Junluo and mother-in-law. (Photo by China Photos/Getty Images)

Joel said documenting the Kazakh nomad summer migration was really an epic journey – a time travel journey – and at the same time was possible to get an understanding of how the balance of nature is still possible in Altai Mountains, Mongolia, June 2015. (Photo by Joel Santos/Barcroft Images)