Advent in the context of "Hanging of the Greens"

A calendrical calculation is a calculation concerning calendar dates. Calendrical calculations can be considered an area of applied mathematics.Some examples of calendrical calculations:

• Converting a Julian or Gregorian calendar date to its Julian day number and vice versa (see § Julian day number calculation within that article for details).
• The number of days between two dates, which is simply the difference in their Julian day numbers.
• The dates of moveable holidays, like Christian Easter (the calculation is known as Computus) followed up by Ascension Thursday and Pentecost or Advent Sundays, or the Jewish Passover, for a given year.
• Converting a date between different calendars. For instance, dates in the Gregorian calendar can be converted to dates in the Islamic calendar with the Kuwaiti algorithm.
• Calculating the day of the week.

Calendrical calculation is one of the five major Savant syndrome characteristics.

A Christmas decoration is any of several types of ornamentation used at Christmas and the greater Christmas and holiday season. Typical images on Christmas decorations include Baby Jesus, Mother Mary, angels, Father Christmas, Santa Claus, and the star of Bethlehem. Advent wreaths, nativity scenes, illuminations, and Moravian stars are popular Christmas decorations.

In many countries, such as Sweden, people start to set up their Advent and Christmas decorations on the first day of Advent. Liturgically, this is done in some parishes through a Hanging of the Greens ceremony. In the Western Christian world, the two traditional days when Christmas decorations are removed are Twelfth Night and if they are not taken down on that day, Candlemas, the latter of which ends the Christmas-Epiphany season in some denominations. Taking down Christmas decorations before Twelfth Night, as well as leaving the decorations up beyond Candlemas, is historically considered to be inauspicious.

The observance of Christmas around the world varies by country and by religion. The day of Christmas, and in some cases the day before and the day after, are recognized by many national governments and cultures worldwide, including in areas where Christianity is a minority religion which are usually found in Africa and Asia. In some non-Christian areas, periods of former colonial rule introduced the celebration (e.g. Hong Kong); in others, Christian minorities or foreign cultural influences have led populations to observe the holiday.

Christmas traditions for many nations include the installing and lighting of Christmas trees, the hanging of Advent wreaths, Christmas stockings, candy canes, setting out cookies and milk, the creation of Nativity scenes depicting the birth of Jesus Christ and giving gifts to others. Christmas carols may be sung and stories told about such figures as the Baby Jesus, Saint Nicholas, Santa Claus, Father Christmas, Christkind or Grandfather Frost. The sending and exchange of Christmas card greetings, observance of fasting and special religious observances such as a midnight Mass or Vespers on Christmas Eve, the burning of a Yule log, and the giving and receiving of presents are also common practice. Along with Easter, Christmas is one of the most important periods on the Christian calendar, and is often closely connected to other holidays at this time of year, such as Advent, the Feast of the Immaculate Conception, Saint Nicholas Day, Saint Stephen's Day, New Year's, and the Feast of the Epiphany.

Advent Sunday, also called the First Sunday of Advent or First Advent Sunday, is the first day of the liturgical year in the Western Christian Churches and the start of the Christian season of Advent; a time of preparation for the celebration of Christ's birth at Christmas and the return of Christ at the Second Coming.

Christmastide, also known as Christide, is a season of the liturgical year in most Christian churches.

For the Catholic Church, Lutheran Church, Anglican Church, Methodist Church and some Orthodox Churches, Christmastide begins on 24 December at sunset or Vespers, which is liturgicus the beginning of Christmas Day. Most of 24 December is thus not part of Christmastide, but of Advent, the season in the Church Year that precedes Christmastide. In many liturgical calendars Christmastide is followed by the closely related season of Epiphanytide that commences at sunset on 5 January—a date known as Twelfth Night.

The Christmas season or the festive season, also known as the holiday season or the holidays, is an annual period generally spanning from November or December to early January incorporating Christmas Day and New Year's Day. The gift-giving associated with the season creates a peak season for the retail sector extending to the end of the period ("January sales"). Christmas window displays and Christmas tree lighting ceremonies are customary traditions in various locales.

In Western Christianity, the Christmas season is traditionally synonymous with Christmastide, which runs from December 25 (Christmas Day) to January 5 (Twelfth Night or Epiphany Eve), popularly known as the 12 Days of Christmas. Christmas in Italy is one of the country's major holidays and begins on 8 December, with the Feast of the Immaculate Conception, the day on which traditionally the Christmas tree is mounted and ends on 6 January, of the following year with the Epiphany. As the economic impact involving the anticipatory lead-up to Christmas Day grew in America and Europe into the 19th and 20th centuries, the term "Christmas season" began to also encompass the liturgical Advent season, the period of preparation observed in Western Christianity from the fourth Sunday before Christmas Day until the night of Christmas Eve. The term "Advent calendar" continues to be widely known in Western parlance as a term referring to a countdown to Christmas Day from the beginning of December.

Christmas lights (also known as fairy lights, festive lights or string lights) are lights often used for decoration in celebration of Christmas, often on display throughout the Christmas season including Advent and Christmastide. The custom goes back to when Christmas trees were decorated with candles, which symbolized Christ being the light of the world. The Christmas trees were brought by Christians into their homes in early modern Germany.

Christmas trees displayed publicly and illuminated with electric lights became popular in the early 20th century. By the mid-20th century, it became customary to display strings of electric lights along streets and on buildings; Christmas decorations detached from the Christmas tree itself. In the United States, Canada and Europe, it became popular to outline private homes with such Christmas lights in tract housing starting in the 1960s. By the late 20th century, the custom had also been adopted in other nations, including outside the Western world, notably in Japan and Hong Kong. It has since spread throughout Christendom.

The Advent wreath, or Advent crown, is a Christian tradition that symbolizes the passage of the four weeks of Advent in the liturgical calendar of the Western church. It is traditionally a Lutheran practice, although it has spread to many other Christian denominations.

It is an evergreen wreath with four candles, sometimes with a fifth, white candle in the center. Beginning with the First Sunday of Advent, the lighting of a candle can be accompanied by a Bible reading, devotional time and prayers. An additional candle is lit on each subsequent Sunday until, by the last Sunday of Advent, all four candles are lit. Some Advent wreaths include a fifth, Christ candle which is lit on Christmas Eve or Christmas Day. The custom originated in family settings but has also become widespread in public worship.

An illumination is an Advent, Christmastide, and Epiphanytide decoration in the form of a lighted candle originating in the Moravian Church. These lighted candles are placed in the windows of Moravian Christian churches and homes in the evening with the symbolism to "guide the footsteps of the infant Jesus" to their settlements. Diane Frantz, a Moravian librarian explicated this, stating that "the Christ child bearing bundles of evergreens wanders all over the world. Those who long for his coming set a lighted candle in the window to welcome him into their home and hearts." Illuminations are first erected on the First Sunday of Advent and are traditionally removed at the end of the Christmastide-Epiphanytide season, which is historically Candlemas. Illuminations are popular in Moravian settlements such as Old Salem, Bethlehem and Lititz, though this custom has spread among the membership of other Christian denominations. In the Moravian town of Herrnhaag, due to the abundance of illuminations there "it appeared from Budingen as though the whole hilltop were a single sea of flames." Brought by Moravian missionaries from Saxony to Bethlehem, illuminations were first used in North America as early as 1741. Though illuminations are traditionally lighted candles, in the modern day, these can be electric candles.