A lot of the airborne particles in the Earth's atmosphere come from natural sources, such as desert dust (red-orange) and sea salt (blue). But there's also soot from fires (green and yellow) and sulfur emissions (white) from burning fossil fuel. William Putman/ NASA/Goddard hide caption

itoggle caption William Putman/ NASA/Goddard

Can you find Australia and Canada? The cartogram scales each country's geographic area by its population. (Click through to see a high-resolution map.) Original work courtesy of Paul Breding. Copyright 2005, ODTMaps.com, Amherst, MA. Adapted by Reddit user TeaDranks hide caption

itoggle caption Original work courtesy of Paul Breding. Copyright 2005, ODTMaps.com, Amherst, MA. Adapted by Reddit user TeaDranks

Wilbur Sargunaraj visits a small house with a thatched roof, a medium-sized house and a "gigantic mansion" in his father's village. Produced by Wilbur Sargunaraj for NPR, John W. Poole and Ben de la Cruz/NPR. hide caption

itoggle caption Produced by Wilbur Sargunaraj for NPR, John W. Poole and Ben de la Cruz/NPR.
Photo Illustration by NPR

Engineering the perfect cookie: You can control the diameter and thickness of your favorite chocolate chip cookies by changing the temperature of the butter and the amount of flour in the dough. Morgan Walker/NPR hide caption

itoggle caption Morgan Walker/NPR
Davar Ardalan/NPR

A young girl stands in the doorway of a home in Uttar Pradesh, India. The markings on the door show that a polio immunization team vaccinated children in the home. Alyce Henson/Courtesy of Rotary International hide caption

itoggle caption Alyce Henson/Courtesy of Rotary International