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As the song goes, Rudolph the Red-Nosed Reindeer had a very shiny nose.
An animal with a nose so bright that it could guide Santa’s sleigh through the night might be a far-fetched belief, but many animals can actually glow through something called bioluminescence.
In particular, the lanterns of anglerfish, the backsides of fireflies and the tentacles on some sea anemones light up through a chemical mashup of two main ingredients: a compound called a luciferin and an enzyme called a luciferase.
“When oxygen is present in the cell, [the pair] react together and give off light,” explained Danielle DeLeo, a marine biologist at Florida International University in Miami, per Science News.
If a reindeer’s nose were to really glow, red would be the best color for it since it has the longest wavelengths of any color we can see, according to Nathaniel Dominy, an evolutionary biologist at Dartmouth College.
“For Rudolph, that red light is going to allow them to navigate under foggy conditions more effectively than any other light,” he said.
However, thanks to science, someone on the ground looking up at a sleigh-pulling reindeer in the sky likely wouldn’t see a nose that looks red at all.
When light sources move toward you, the light waves squish together and appear bluer, and when they move away, the waves stretch and look redder — though things have to travel very fast for the color shift to occur.
Laura Driessen, a radio astronomer at the University of Sydney, suggested that Santa’s sleigh could be an exception since it would have to be traveling at an extreme speed to hit multiple houses worldwide in just one night.
If Santa and his sleigh traveled at 10% the speed of light, Rudolph’s nose would be blueshifted to look orange as he approaches a house and would redshift to “nearly the deepest crimson red that human eyes can see” — almost black — as he flies away.
It would also take a lot of energy for Rudolph to travel so fast and shine his nose so bright.
“I would want to make sure that he could get as much energy as possible — sugary foods,” Dominy noted. (So maybe leave out extra cookies for Santa’s reindeer, too.)
While Rudolph’s built-in red light would make a great headlight for Santa’s sleigh, DeLeo said that the odds of bioluminescence evolving in reindeer are “very, very low,” considering most glowing animals are found in the ocean, and the land animals that do glow are not mammals.
But it’s not impossible.
“[Bioluminescence] evolved at least 100 times across the tree of life,” DeLeo noted.
