Rudolph could use something many organisms use on Earth in order to create natural light -- a neat little scientific trick called bioluminescence. Animals can make their own light by mixing certain chemical compounds together to produce a glow. The reasons vary -- fireflies, for instance, flash light at each other in order to attract mates, while some fish that live very deep in the ocean use light to locate prey.
There would be three parts to his nasal beacon. The first would be just like any other reindeer nose (so his playmates technically shouldn't have shunned him from any reindeer games in the first place). He would breathes oxygen through it, and it would be made up of two layers -- the dermis, the thick, inner layer of skin that contains blood vessels and hair follicles, and the epidermis, the thin, outer layer that you can see and touch. The other two parts, however, would set Rudolph apart from all the other reindeer.
The second part is a thin, enclosed layer of a light-producing organ between the dermis and the epidermis. Inside this layer is luciferin, a light-producing substance, and luciferase, an enzyme that catalyzes the light-producing reaction.
The third part is where the "red-nosed reindeer" part comes in. Most bioluminescent life forms, like fireflies, produce green light. The outermost part of Rudolph's nose, however, would be a red phosphorescent layer -- once the light-producing organ started creating light, the phosphorescent part of his nose would absorb the green light and emit a red light.
How would his nose get so bright, though? Bioluminescence often requires another substance, like oxygen, to make light, and Rudolph would breathe lots of oxygen right near the light-producing organs, providing enough reactions for long, intensely shiny bursts of light.
But why is Rudolph the only reindeer with a nose that glows? In the next section, we'll learn about how and why Rudolph has a muzzle like no other.