National Geographic Magazine April 2021

IT’S HARD TO IMAGINE places more different from one another than Delhi, India; Mexico City, Mexico; and Gary, Indiana. Yet years after I visited those cities, they’re indelibly linked in my memory for one reason: the foul, polluted air smothering their landscapes. The pollution was so heavy you could see it wafting through the interiors of modern buildings (Delhi, 2016), feel it stinging your eyes (Mexico City, 1972), and smell it through closed car windows (Gary, the 1960s). Despite its ubiquity, or perhaps because of it, air pollution has rarely gotten the sustained attention it deserves. That’s an outrage, given that air pollution is a global killer, causing an astonishing seven million premature deaths every year. But it’s also an opportunity, because this is an environmental problem that we actually can…

LOOKING AT THE EARTH FROM EVERY POSSIBLE ANGLE With chalkboard as canvas, mathematicians create new forms of language and art.…

DETRACTORS MAY deride mathematics as difficult, abstract, rigid, boring. But to admirers, mathematics is fascinating, creative, even an art form—and its canvases are chalkboards covered with scribbles, an odd mix of therapy and ingenuity known as board work Photographer Jessica Wynne learned about the beauty of mathematics from her summer neighbors on Cape Cod, Massachusetts. Both of them are theoretical mathematicians, and when their friends—also theoretical mathematicians—came over, Wynne noticed that chalkboard ponderings were how they communicated complex ideas and worked out knotty problems. They used chalkboards to collaborate and spar and, most of all, to explore the boundaries of known mathematics. Some described it as meditation. In a world with plenty of paper, whiteboard, and digital screen space, why chalk? “That’s like asking a painter why they paint with oils,” says…

IN THIS SECTION Parakeet Invasions Selfies on Everest Teapot Diplomacy Perfumers’ Alchemy ILLUMINATING THE MYSTERIES—AND WONDERS—ALL AROUND US EVERY DAY BEFORE MY HUSBAND AND I moved to San Francisco, we lived in Southern California, in a glistening beach town along the coast a few miles south of Los Angeles International Airport. The yard of our ranch-style house opened onto a half-acre-wide easement overgrown with fennel, sage scrub, and wild mustards. It was city-owned land, permanently set aside as open space, and soon after moving in, I “borrowed” some for a vegetable garden. I cleared the land by hand, ordered a truckload of topsoil, then built 14 10-by-12-foot raised beds in which I planted heirloom tomatoes, cucumbers, carrots, green beans, beets, and leafy greens. My parents lived three blocks away. In the evenings after work, and often…

Teresa Zgoda was home from college, where she was studying science photography, when a turtle that had been hit by a car was brought to her dad’s animal hospital in New York State. The turtle had lost most of one foreleg—and an x-ray showed that it was pregnant. Though the turtle survived to lay her eggs, none hatched. But Zgoda, using editing and colorizing tools, turned the x-ray into a science lesson—illuminating details of the turtle’s anatomy and eggs—and a piece of art. X-RAY IMAGE: OTTERKILL ANIMAL HOSPITAL, CAMPBELL HALL, NEW YORK…

DISPATCHES FROM THE FRONT LINES OF SCIENCE AND INNOVATION Light-as-air solar collectors In solar cell technology, what does ultralightweight mean? Thin and flexible enough to rest on a soap bubble. The cells can capture energy from indoor or outdoor light, their makers say, and could help power medical skin patches, sensors for drones, and other devices too slight for heavy batteries. —JS IT SEEMS INCONGRUOUS: fluorescent-green tropical birds totally at home in a park in Hesse, Germany (above). Are they fugitives from a tearoom or a pirate ship? No—just opportunistic avians that escaped or were released into the wild and quickly multiplied. Rose-ringed parakeets, native to South Asia, were sold as pets until trade in wild birds was banned in the U.S. and Europe. Now they and monk parakeets have gone from pet to pest…