The hardworking AERONET (AErosol RObotic NETwork) instrument in Baengyeong, South Korea was having a rough day. Every 15 minutes, the telescope-like device pointed its barrel at the sun to record its light and measure how much was blocked by airborne particles, or aerosols. July 13, 2012 was an overcast day and the light absorbed by the clouds dominated the measurements. But then, just after 1 p.m., the clouds parted, the instrument looked up, and data was collected. Only no one saw it.