Around the world, big cities and small towns alike brighten during the holiday season. From extravagant decorations to house lights, to towering trees of the Rockefeller kind, the planet illuminates in a spectacular showcase of celebration – and space has a front row seat.
Surprising new images from space reveal that lights across the United States shine 20 to 50 percent more brightly in December than they do the rest of the year, NASA researchers reported. Similarly, some cities in the Middle East illume by more than 50 percent during the Muslim holy month of Ramadan.
“What’s happening during the holidays is that our patterns are changing,” study co-leader Miguel Roman, of NASA’s Goddard Space Flight Center in Greenbelt, Maryland, said during a press conference at the annual fall meeting of the American Geophysical Union.
“People are leaving work for the holiday, and they’re turning on the lights,” he said, adding that researchers had previously believed that nighttime lights were comparatively stable throughout the year. “People are demanding more energy services, and we see that embedded in this data.”
Roman and his peers studied information collected in 2012 and 2013 by the Visible Infrared Imaging Radiometer Suite (VIIRS) instrument aboard the Suomi NPP (National Polar-orbiting Partnership) satellite, a mission that involves both NASA and the U.S. National Oceanic and Atmospheric Administration. The researchers were able to create a new algorithm that removed clouds and moonlight in the VIIRS data, allowing them to pinpoint city lights and keep an eye on how they changed over time.
Altogether, the team looked at 70 warm American cities, all south of St. Louis, since snow was too reflective for the algorithm to handle. Every one of the 70 points – including areas in Puerto Rico – lit up just after Thanksgiving and shined brightly through January 1st, Roman said.
“This is telling us something that we all as Americans know, which is that Christmas is not just a religious holiday; it is also a civic holiday,” he said. “This space-based retrieval is tracking this national tradition. It’s amazing.”
A homogenous pattern was also observed throughout the Middle East during the Ramadan holiday, which is in the ninth month in the Islamic calendar. During the occasion, many Muslims fast during the daylight hours and delay meals and a number of other activities until nightfall; thus, cities in Muslim countries such as Jordan and Egypt exhibited the brightness spike during Ramadan.
Yet, lights in neighboring Israel remained stable throughout the year, showing that the VIIRS data can track cultural differences as well, researchers said.
“These nighttime lights really are in some ways the EKG of a city,” said study co-leader Eleanor Stokes, a Ph.D. candidate at Yale University.
Stokes added that the study’s results, as well as the research team’s approach, could help scientists better understand energy demand, and resultantly help in figuring out more efficient ways to deal with climate change.
“What we found here is that energy service demand is the aggregate of human activity, and human activity is driven not just by individual factors like price — like energy and electricity prices — but also, activity is driven by social and cultural context,” she said. “When you look at the energy signatures, you can see those imprints, those cultural and social imprints.”