After Hurricane Maria tore across Puerto Rico, it quickly became clear that the destruction would pose daunting challenges for first responders. Most of the electric power grid and telecommunications network was knocked offline. Flooding, downed trees, and toppled power lines made many roads impassable.In circumstances like this, quickly knowing where the power is out—and how long it has been out—allows first responders to better deploy rescue and repair crews and to distribute life-saving supplies. And that is exactly why teams of scientists at NASA are working long days to make sure that groups like the National Guard and the Federal Emergency Management Agency (FEMA) get high-quality satellite maps of power outages in Puerto Rico.These before-and-after images of Puerto Rico’s nighttime lights are based on data captured by the Suomi NPP satellite. The data was acquired by the Visible Infrared Imaging Radiometer Suite (VIIRS) “day-night band,” which detects light in a range of wavelengths from green to near-infrared, including reflected moonlight, light from fires and oil wells, lightning, and emissions from cities or other human activity.