In 1868 Swedish physicist Anders Ångström discovered that the sky always has a slight glow to it. The light emanates from molecules excited by sunlight or cosmic rays in the upper atmosphere. At night, the amount of airglow is comparable to the light from the full moon spread over the entire sky. But because most of it lies in the short-wave infrared range, the light remains largely invisible—at least to human eyes. Researchers have now devised a camera that could effectively detect this glow to see in the dark better than ever before.