The holiday spirit can now be quantified and measured -- as a brightening of nighttime lighting so distinctive that, if you have the right technology to observe it, is visible from space.
For instance, here's what the D.C.-Baltimore area looks like (anything colored green means there is more nighttime light at this time of year than in other seasons):
The image above is based on data from the Suomi National Polar-orbiting Partnership (NPP) satellite, whose Visible Infrared Imaging Radiometer Suite (VIIRS), capable of glimpsing the side of the Earth that is facing away from the sun, is responsible for the famous "Earth at Night" pictures that we've all seen before.
So what's the reason for increased lighting? It's simple, says NASA's Miguel Román, a physicist at the NASA Goddard Space Flight Center who conducted the research behind the images with Eleanor Stokes, a NASA fellow and Ph.D. student and at Yale. "What you’re seeing here, anywhere you see green, is Christmas lights from space," says Román.
"If you look at the spatial trend, you will find, a lot of the green in the DC area is concentrated in the suburbs," he adds.
Here are Los Angeles, San Diego, Phoenix, and Las Vegas:
The composite images are based on the period from the end of Thanksgiving through the first week of January. Only cities not under regular snowfall in winter could be imaged in this way (snow reflects light).
Overall, the researchers found that nighttime lighting increased by 20 to 50 percent in U.S. cities and suburbs during the holiday period, and that suburbs tended to light up more than urban centers. The images are based on data from 2012 and 2013.
Here are Atlanta, Charlotte, Birmingham, and Nashville:
And the holiday light-up isn't just an American phenomenon. The researchers also looked at predominantly Muslim cities celebrating Ramadan, a month of fasting that shifts its date each year, due to the lunar Islamic calendar. Here, they examined three years, from 2012 through 2014, and saw a marked lighting increase in Cairo:
This time, of course, the lighting isn't Christmas lights. Rather, it's people changing their schedules due to the religious holiday. "It’s a change in the timing of human activity, because people are fasting from dawn to dust," says Yale's Eleanor Stokes. "So activity, commerce, heating, family gatherings are all being pushed later into the night."
The Cairo picture shows something else interesting as well, notes Stokes -- economic differences. The researchers found that in poorer areas, people were still celebrating Ramadan but were not using more energy at night, presumably instead choosing to conserve and save money.
Something similar appeared elsewhere in the Muslim world. Devout Saudi Arabian cities like Riyadh saw an up to 100 percent increase in lighting:
However, the researchers also saw variability across the Muslim world. Istanbul, Turkey, which is more secular, did not increase its lighting as much during Ramadan:
The upshot of this, says NASA's Román, is that you can see, in the images, just how differently people in Istanbul behave, during Ramadan, than do people in Cairo or Riyadh.
"We can map culture from space," says Román.