In his masterful Adoration of the Magi, completed in 1304, the Florentine painter Giotto di Bondone reproduced the iconic Christmas scene where the travelers from the East meet baby Jesus. Up in the sky, the Star of Bethlehem is depicted as a bright golden comet. Giotto had witnessed the appearance of Halley's Comet in 1301 and the event clearly impressed him deeply.
What he didn't know is that the comet had also appeared in 12 BCE. There were other comets sightings around the time, as cataloged in David Hughes's book The Star of Bethlehem: An Astronomer's Confirmation.
Giotto's connection between comet and the auspicious star was derided by many, including Thomas Aquinas (the reader interested on the eschatology of comet lore can consult my book The Prophet and the Astronomer). Comets don't shine during the day, he argued, and furthermore comets were a bad omen, not a good one: "On the seventh day all the stars, both planets and fixed stars, will throw out fiery tails like comets," he wrote.
In any case, the relation between the prophetic nature of cosmic events and astronomical phenomena runs deep in most cultures of the world. If the skies are the realm of God or the gods, they will mirror divine intentions, be they good or bad.
The great German astronomer Johannes Kepler, trying to explain the Biblical event in scientific terms, determined that Jupiter and Saturn approached each other three times in the year 7 BCE. He conjectured that planetary conjunctions could create a nova, which at the time was thought to represent the birth of a new star in the sky.
(We now know that a nova is related to the cataclysmic outburst of energy that happens when a white dwarf star accretes matter from a companion star. As the pressure mounts and the temperature achieves a certain threshold, the accreted material, mostly hydrogen, fuses into helium in an explosive manner. From the Earth, it appears that the star's luminosity is greatly increased for periods varying from 25 to 100 days.)
There have been many attempts at trying to relate the Star of Bethlehem to an astronomical event. In the lack of strong evidence, caution should be used in pinning one down.
Caution should also be exercised when relating flying reindeer to the effects of the hallucinogenic (actually a deliriant) fly agaric mushroom, or Amanita Muscaria, which was, and presumably still is, consumed during shamanic rituals by the Lapps and some Siberian peoples. The mushroom is the quintessential toadstool, usually bright red with small white spots and has long been depicted in stories and paintings. Among its many nicknames, my favorite is the Italian ovolo matto (mad egg) from Trentino.
The ethnobotanist Jonathan Ott has even speculated that the red and white colors of the mushroom inspired the colors of Santa Claus's outfit and that the flying reindeer comes from the bizarre behavior of the animals after ingesting it.
Popular culture — of religious inspiration or not — is a rich repository of human experiences and narratives, much of it the result of what people see (or think they see) and feel (or think they feel). That science can shed some light into their origins only adds to their allure. I will hang an Amanita Muscaria decoration to our Christmas tree this year. The Star of Bethlehem, of course, is already at the top.