File:Snow in the Mountain West (MODIS 2024-12-25).jpg

English: Winter was in full swing in the Rocky Mountains in mid-December 2024, with a deep layer of snow piled atop the ranges of Idaho, Utah, and Wyoming. On December 17, western Wyoming was under a Winter Weather Warning, with heavy snow expected. And on December 18, Brundage Mountain Resort, a ski resort located in Idaho, reported 5 inches (12.7 cm) of new snow fall. They excitedly tweeted that they had reached the milestone of 100 inches of snow for the 24/25 season, with a snowfall total of 102 inches in the base area and 114 inches at Lakeview. The resort reached 100 inches of snow on February 3 in the 23/24 season.

The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite acquired this false-color image of the region on December 19, after a snowstorm dropped several inches in the high mountains.

By using blue and shortwave infrared light (MODIS bands 3,6,7) to highlight the different reflectivity of snow, ice, clouds, and vegetation, the image lights up in green and red. The bold green marks area of vegetation while bright red or orange marks highly reflective and cold snow or ice. Liquid water would appear deep red or black, while clouds appear white or, if they contain ice crystals, may take on a tint of peach. Snow blowing over Utah’s Great Salt Lake, which can be seen just south of center in this image, creates orange-red bands across the water.

The overall all red/green coloration of this image is appropriate for the Christmas holiday, which is celebrated on December 25 in the United States and many other countries. Each year, many Americans cloak their homes and hearths in reds and greens as they celebrate Christmas, which is foundational to the Christian religion but is also a popular secular celebration. These colors have become intertwined with the seasonal celebrations for as many years as anyone living can recall, although the exact reason they mark a Christian holy day isn’t exactly clear. Some sources suggest religious symbolism, with red representing the blood of Christ and green reminding of the “eternal life” of the evergreen trees that stand resplendent in the harshest winter. Others believe that the colors come from the green leaves and bright red berry of the holly tree—a stunning plant at its most showy during mid-December. Kids might say it’s from the bright red nose of Rudolph, the reindeer who is said to pull Santa’s sleigh on Christmas Eve, and the deep green of the traditional Christmas tree.

For scientists looking at false-color satellite imagery, however, reds and greens have nothing to do with Christmas, and everything to do with the reflectance of various features on Earth, as today’s striking Image of the Day illustrates.