They may not have sorted out how Santa's reindeer can fly, but scientists say there is an optical explanation for just how beneficial it is that Rudolph's nose burns red and bright. Reporting in the journal Frontiers for Young Minds, a Dartmouth anthropology professor says that Arctic reindeer are (at least among mammals) uniquely qualified to see ultraviolet light—a useful trait in the darker winter months when the sun is low on the horizon and casts more UV light than usual. The reflective tissue in their eyes turns a deep blue to help them see in the dark. The problem is fog extinguishes this hue, reports Phys.org. Rudolph's glowing red nose, then, solves this conundrum when it's time to steer Santa's sleigh through the fog. Unfortunately, that red nose comes with an unfortunate side effect.
Because reindeer's noses are so vascular, a glowing one would likely cause excessive heat loss with potential for hypothermia. "It is therefore imperative for children to provide high-calorie foods to help Rudolph replenish his energetic reserves on Christmas Eve," the anthropologist advises. While he adds that the frequency of fog is on the decline thanks to climate change, kids can still help the reindeer's odds by providing chocolate chip cookies in case Santa's team encounters any on the big night, reports Red Orbit. Another hypothesis floating around is that Rudolph’s nose is infected—and thus inflamed—with parasites. "Such contrasting hypotheses invite testing," reports the PLoS Ecology blog, "and it is hoped that future research on the optical properties of Arctic light and fog will shed, dare I say, new light, on the extraordinary biology and sensory ecology of reindeer." (Check out how fast Rudolph has to fly.)