Christmas

Christmas is an annual festival, commemorating the birth of Jesus Christ, observed primarily on December 25 as a religious and cultural celebration among billions of people around the world. A feast central to the Christian liturgical year, it is preceded by the season of Advent or the Nativity Fast and initiates the season of Christmastide, which historically in the West lasts twelve days and culminates on Twelfth Night; in some traditions, Christmastide includes an octave. Christmas Day is a public holiday in many of the world's nations, is celebrated religiously by a majority of Christians, as well as culturally by many non-Christians, and forms an integral part of the holiday season centered around it.

Although the month and date of Jesus' birth are unknown, December 25 - a date close to the Winter Solstice - was already popular in the Roman Empire as the birthday of several Sun gods including Mithras. By the early-to-mid 4th century, the Western Christian Church had fixed the date of Christmas as December 25, a date that was later adopted in the East. Today, most Christians celebrate on December 25 in the Gregorian Calendar, which has been adopted almost universally in the civil calendars used in countries throughout the world. However, some Eastern Christian Churches celebrate Christmas on December 25 of the older Julian Calendar, which currently corresponds to January 7 in the Gregorian calendar, the day after the Western Christian Church celebrates the Epiphany. This is not a disagreement over the date of Christmas as such, but rather a preference of which calendar should be used to determine the day that is December 25. Moreover, for Christians, the belief that God came into the world in the form of man to atone for the sins of humanity, rather than the exact birth date, is considered to be the primary purpose in celebrating Christmas.

Literary comment
Characters in numerous Harry Turtledove works celebrate Christmas, but this rarely provides insight into any particular story.

Christmas in Ruled Britannia
The Spanish conquerors of England imposed the Gregorian calendar on the nation in place of the older Julian one. An effect of this was that the date which the English had traditionally regarded as 25 December, the feast of the Nativity, was now considered to be 4 January. As the old calendar was considered a sign of now-outlawed Protestantism, adherents to the old dating system, who wished to continue celebrating Christmas on the old date, had to do it in secret, away from the notice of the English Inquisition.

On 25 December 1597, Lieutenant Lope de Vega was sent by Captain Baltasar Guzmán to make sure that William Shakespeare attended Mass at St. Ethelberge's on the correct date. Vega was pleased to observe and report in the affirmative.