You're helping make the world a brighter place just by switching on your Christmas lights. New data shows many US cities brighten by 20% to 50% between Thanksgiving and New Year's Day, and it's all visible from space, Wired reports. A research team used a NASA-NOAA satellite camera—sensitive enough to pick up "the faintest signal like a fishing boat," scientist Miguel Roman tells Smithsonian—to photograph 70 US cities every night at 1am local time from 2012 to 2013. (They picked cities free of snow, which disrupts readings.) Many got brighter in December. Researchers then plotted their findings on a map: Red dots show a darker area compared to the rest of the year, yellow dots show no change, and green dots indicate a boost in brightness.
The brighter areas tend to be "in the suburbs and the exurbs and the periphery," says Roman. Why? "People are leaving work for the holidays and they're turning on the lights." But the trend isn't restricted to December, or to the US. Some Middle Eastern cities get 50% brighter during the month of Ramadan, Space.com reports. Cities in Jordan and Egypt especially lit up as activity shifted to later at night, while those in Israel and other countries saw no change. This could indicate unstable electrical grids, cultural differences, or conflict, researchers say. Interestingly, they found nighttime brightness fell 94% in Aleppo, Syria, following a major battle in July 2012. The study as a whole will help experts track carbon emissions and energy demands. (Your holiday decorations probably came from this town in China.)