Revelation Day, the Epiphany

In the World of Athena Minerva, people of Scandinavian descent celebrate a very peculiar holiday which appeared for many years to celebrate a time-travel event of intense controversy by scientists before it was debunked.

Revelation Day

Celebration

On Revelation Day it is traditional to trade trivia and interesting factoids with each person when one first meets them that day, family, friends, and total strangers. Some celebrants research the night before to pick a piece of esoteric knowledge which will impress their peers and verify the veracity of the information. Often two items are chosen, one for quick meetings, and another that may take a large portion of a meal together to fully explain. Some pick an innocent piece of trivia and a more naughty suggestive item so that they may use the more appropriate one for the audience.
Some choose instead to spread jokes which sound like trivia, making their celebration similar to April Fool's Day. Such as:

If you laid every bone in a man's body end to end... he would probably die.

Calendar

Revelation Day is celebrated on one of two days depending on local tradition.

1. The simplest way to calculate the day is just to make it the 6^th of January. This was common in more industrial areas. The day is barely celebrated in such areas, much like April Fools' Day. The underpinning reason was to place the celebration after the Twelfth Night after Christmas Day.
2. More agricultural areas set the day as the first Sunday of each new year. In these areas an elaborate Sunday church celebration among Christians involves driving the tractors of the congregants (frequently just one symbolic tractor) to the front of the local church where it is used to bestow a blessing upon all those present at the start of the agricultural year. It is also colloquially called "Plough Sunday", which is followed by the first day of work preparing fields to plant new crops on "Plough Monday".

History clouded in myth

Before history combined Revelation Day with other celebrations, it was used as a day to remember Saint Ingrid and her heroic battles and sacrifices. Unlike other saints, it was not the day of her death nor martyrdom. Instead the celebration reportedly took place each year on the day Saint Ingrid's husband became a believer in her prophesies and committed himself and his military forces to her cause.
The first recorded celebration of Revelation Day was not until 100 years after the event it celebrates, so the exact day and year may have been lost to historians.
It was said that on January 6th, AD 1000, that the woman who would become Saint Ingrid (also known by vikings as "Valkyrie, Chooser of the Slain") whipped up the soldiers in her husband's entourage into such a fighting frenzy that they not only exceeded the might and savagery of the already legendary Berzerkers but actually continued fighting after several limbs had been bitten off by an attacking herd of Catoblepas, the creatures also being legendary creatures from Greek mythology among others, something like a dinosaur, and resembling a long-necked buffalo.
After winning the battle, the story says that her husband, the viking of noble lineage, Målmann, (a name meaning "target man", "man who always hits the target", or "man with a target on his back") knelt down before her announcing that he had never seen such leadership on any battlefield. He renewed his wedding vows to her on the spot, with one exception. Originally, she had vowed to follow his leadership. This time he vowed to obey hers, which was "a thing unheard of" in their society at the time.
Her legends state that a few days earlier, her husband accommodated her to hunt a maneating beast. After a quick pep talk from her, her two servants fought and killed a rampaging Yeti in a snowstorm, naked. One of her servants lost an arm in the fight, and the legend says that she popped the Yeti's arm onto his stump, and her faith or magic was so great that it healed in place, and both servants survived.
Thge legends go on to say that the couple sailed the world (incidentally, with her in the lead in matriarchal lands and him in patriarchal ones) dispatching at least one dragon, sea serpents, and the like, and our world is free of such legendary maneaters to this day as a result of their work.
Her last and perhaps her most dramatic alleged miracle was calling down "her star" from the sky to crash into an advancing army of near-feral man beasts bent on the destruction of the human race (which was lead by the three witches who had created all the vicious maneaters that Saint Ingrid had previously dispatched). The falling star destroyed them all and left a massive crater. Since then many craters across the Scandinavian countries have been associated as "Saint Ingrid's Crater" by believers.
The part of the legend which disturbs historians is her alleged claim that she used neither magic nor holiness but secret knowledge that our world would discover in a thousand years. She claimed to be from another world of tremendously more advanced science. Some historians note this as the invention of the concept of time travel, others of the concept of dimension travel. Many of humanity's earliest legends seem to speak of interplanetary travel, so this story is unremarkable if that is the interpretation. Regardless, all of her miracles could be reproduced with technology roughly 1100 years later.

Conflagrated Holidays

Revelation Day is also called the "Feast of the Epiphany", "Plough Sunday" (as noted above), the "Visit of the Magi to the Christ Child", and "Three Kings' Day".