Satellite images of nighttime lights, normally used to detect population centers, also can help keep tabs on diseases in developing nations, according to new research. An international research team that includes Matthew Ferrari, assistant professor of biology at Penn State, found that the composited images accurately indicate fluctuations in population density—and thus the corresponding risk of epidemic—that can elude current methods of monitoring outbreaks. The research is expected to help medical professionals synchronize vaccination strategies with increases in population density.