Years ago, Christopher Kyba was skeptical about astronomy data collected by citizen scientists—after all, it relies on people making naked-eye assessments of the night sky. But when a student wrote to him with a question about measuring the sky’s brightness, he thought of the Globe at Night citizen science project, which launched in 2006 to let students track the stars they could see. He downloaded and pored over the data. “I became a complete convert,” says Kyba, a scientist at the German Research Center for Geoscience in Berlin. He has since devoted his career to studying light pollution and has now analyzed Globe at Night data from around the world to quantify its astonishing rise in recent years.