The winter solstice, or hibernal solstice, occurs when either of Earth's poles reaches its maximum tilt away from the Sun. This happens twice yearly, once in each hemisphere (Northern and Southern). For that hemisphere, the winter solstice is the day with the shortest period of daylight and longest night of the year, and when the Sun is at its lowest arc in the sky. In each polar region, there is continuous darkness or twilight around its winter solstice. The opposite event is the summer solstice, which happens at the same time in the opposite hemisphere.

The winter solstice occurs during the hemisphere's winter. In the Northern Hemisphere, this is the December solstice (December 21 or 22) and in the Southern Hemisphere, this is the June solstice (June 20 or 21). "Although the winter solstice itself occurs at a specific moment in time, the term is also commonly used to refer to the day on which it occurs." Traditionally, in many temperate regions, the winter solstice is seen as the middle of winter, and "midwinter" is another name for the winter solstice, although it carries other meanings as well. Other names are the "extreme of winter", the "shortest day" and the "longest night".

Since prehistory, the winter solstice has been a significant time of year in many cultures and has been marked by festivals and rites. "This is because it marks the point when daylight hours stop decreasing and begin to increase again." In parts of Europe it was seen as the symbolic death and rebirth of the Sun. Some ancient monuments such as Newgrange, Stonehenge, and Cahokia Woodhenge are aligned with the sunrise or sunset on the winter solstice.

History and cultural significance The winter solstice is the reversal of the Sun's apparent ebbing in the sky; the daytime stops becoming shorter and begins to lengthen again. In parts of ancient Europe, this was symbolized as the death and rebirth of the Sun, or of a Sun god.Krupp, E C. Echoes of the Ancient Skies: The Astronomy of Lost Civilizations. Courier Corporation, 2012. pp. 119, 125, 195North, John. Stonehenge. The Free Press, 1996. p. 530Hadingham, Evan. Early Man and the Cosmos. University of Oklahoma Press, 1985. p. 50

There is evidence that the winter solstice was deemed an important time of the yearly cycle for some cultures as far back as the Neolithic (New Stone Age). Astronomical events were often used to guide farming activities, such as the sowing of crops and mating of animals. Livestock were slaughtered so they would not have to be fed during the winter, so it was almost the only time of year when there was a plentiful supply of fresh meat for feasting.

Neolithic Europe

Some important Neolithic and early Bronze Age archaeological sites in Europe are associated with the winter solstice, such as Stonehenge in England and Newgrange in Ireland (for others see List of archaeoastronomical sites by country). The primary axes of these two monuments seem to have been carefully aligned on a sight-line pointing to the winter solstice sunrise (Newgrange) and the solstice sunset (Stonehenge). Newgrange was built with a "light box" so that direct sunlight reaches the inner chamber only on the winter solstice. At Stonehenge, the great trilithon, the Heel Stone and the avenue are aligned to the winter solstice sunset. The Neolithic Goseck Circle in Germany has two openings, aligned with the winter solstice sunrise and sunset respectively.

Ancient Egypt

Several ancient Egyptian temples are aligned with the winter solstice sunrise, including the Temple of Amun-Ra at Karnak, the chapel of Ra-Horakhty at Abu Simbel, and the Mortuary temple of Hatshepsut at Luxor.

Plutarch wrote in the Moralia (first century AD) that the Egyptians believed the goddess Isis gave birth to Harpocrates (Horus the Child) at the winter solstice.Plutarch. Moralia, with an English translation by Frank Cole Babbitt. Harvard University Press, 1936. Macrobius wrote in the fourth century that the Sun appears small at the winter solstice, and on this shortest day, the Egyptians brought an idol of a child Sun god out of a shrine. In his Panarion, also from the fourth century, Epiphanius of Salamis wrote that the winter solstice was celebrated on 25 December in Alexandria as the Kikellia. Epiphanius says that thirteen days after the solstice, on 5–6 January, they celebrated the birth of Aion, son of the virgin goddess Kore. At the temple of Kore (the Koreion) in Alexandria, an all-night vigil was held, and at dawn an idol of the child god was brought out of an underground shrine. This idol was carried around the temple seven times, accompanied by music, hymns and revelry.

Ancient Roman world

In the ancient Roman calendar, December 25 was the date of the winter solstice. Marcus Terentius Varro wrote in the first century BC that this was regarded as the middle of winter. In the same century, Ovid wrote in the Fasti that the winter solstice is the first day of the "new Sun".Ovid, Fasti, translated by A. Wiseman and P. Wiseman. Oxford University Press, 2013, p.5 The Calendar of Antiochus of Athens, second century AD, marks it as the "birthday of the Sun". In AD 274, the emperor Aurelian made this the date of the festival , the birthday of Sol Invictus or the 'Invincible Sun'. Gary Forsythe, Professor of Ancient History, says "This celebration would have formed a welcome addition to the seven-day period of the Saturnalia (December 17–23), Rome's most joyous holiday season since Republican times, characterized by parties, banquets, and exchanges of gifts".

Liturgical historians generally accept that the winter solstice had some influence on the choice of December 25 as the date of Christmas. A widely-held theory is that the Church chose it as Christ's birthday () specifically to appropriate the Roman festival of the sun god's birthday (). According to C. Philipp E. Nothaft, a professor at Trinity College Dublin, though this "is nowadays used as the default explanation for the choice of 25 December as Christ's birthday, few advocates of this theory seem to be aware of how paltry the available evidence actually is".

Germanic

In the sixth century, the Greek historian Procopius wrote that the people of Scandinavia (which he calls Thule) held their greatest festival shortly after the winter solstice, to celebrate the return of daylight.

In Anglo-Saxon England the winter solstice was generally deemed to be December 25, and in Old English, midwinter could mean both the winter solstice and Christmas. In the eighth century, Bede wrote that the pagan Anglo-Saxons had celebrated the festival ('Mothers' Night') at the winter solstice, which marked the start of the Anglo-Saxon year.

Bede also wrote that the pagan Anglo-Saxons called both December and January Giuli. Bede links this term with the winter solstice, writing that "The months of Giuli derive their name from the day when the Sun turns back [and begins] to increase". This is an Old English form of the word 'Yule', and it is also spelled , and . Other Old English writers call December Ǣrra Geōla (the former Yule) and January Æftera Geōla (the latter Yule).Bosworth, Joseph. "Geóla". In An Anglo-Saxon Dictionary Online, edited by Thomas Northcote Toller, Christ Sean, and Ondřej Tichy. Prague: Faculty of Arts, Charles University, 2014.

The North Germanic peoples celebrated a winter holiday called , the Old Norse form of the word 'Yule'. The Heimskringla, written in the 13th century by the Icelander Snorri Sturluson, describes a feast hosted by the Norwegian king Haakon the Good (c. 920–961). According to Snorri, the Christian Haakon had moved from "midwinter" and aligned it with Christmas. This led some scholars to believe that Scandinavian Yule () originally was a sun festival on the winter solstice. Modern scholars generally do not believe this, as the medieval Icelandic "midwinter" () was about four weeks after the solstice. During the Christianisation of the Germanic peoples, Yule was incorporated into the Christmas celebrations and the term and its cognates still refer to Christmas in modern Northern European languages such as Swedish.

Albanian Albanian traditional festivities around the winter solstice celebrate the return of the Sun (Dielli) for summer and the lengthening of the days. pp. 43–71. pp. 249–251. The Albanian traditional rites during the winter solstice period are pagan, and very ancient. Albanologist Johann Georg von Hahn (1811 – 1869) reported that Christian clergy, during his time and before, have vigorously fought the pagan rites that were practiced by Albanians to celebrate this festivity, but without success.

The old rites of this festivity were accompanied by collective fires (zjarre) based on the house, kinship or neighborhood, a practice performed in order to give strength to the Sun according to the old beliefs. The rites related to the cult of vegetation, which expressed the desire for increased production in agriculture and animal husbandry, were accompanied by animal sacrifices to the fire, lighting pine trees at night, luck divination tests with crackling in the fire or with coins in ritual bread, making and consuming ritual foods, performing various magical ritualistic actions in livestock, fields, vineyards and orchards, and so on.

Nata e Buzmit, "Yule log's night", is celebrated between December 22 and January 6. Buzmi is a ritualistic piece of wood (or several pieces of wood) that is put to burn in the fire (zjarri) of the hearth (vatër) on the night of a winter celebration that falls after the return of the Sun for summer (after the winter solstice), sometimes on the night of Kërshëndella on December 24 (Christmas Eve), sometimes on the night of kolendra, or sometimes on New Year's Day or on any other occasion around the same period, a tradition that is originally related to the cult of the Sun.

East Asian

In East Asia, the winter solstice has been celebrated as one of the Twenty-four Solar Terms, called Dongzhi (冬至) in Chinese. In Japan, in order not to catch cold in the winter, there is a custom to soak oneself in a yuzu hot bath ( = Yuzuyu).

Indian

Makara Sankranti, also known as Makara Sankrānti (Sanskrit: मकर संक्रांति) or Maghi, is a festival day in the Hindu calendar, in reference to deity Surya (sun). It is observed each year in January. It marks the first day of Sun's transit into Makara (Capricorn), marking the end of the month with the winter solstice and the start of longer days.

Iranian

Iranian people celebrate the night of the Northern Hemisphere's winter solstice as, "Yalda night", which is known to be the "longest and darkest night of the year". Yalda night celebration, or as some call it "Shabe Chelleh" ("the 40th night"), is one of the oldest Iranian traditions that has been present in Persian culture from ancient times. In this night all the family gather together, usually at the house of the eldest, and celebrate it by eating, drinking and reciting poetry (esp. Hafez). Nuts, pomegranates and watermelons are particularly served during this festival.

Judaic An Aggadic legend found in tractate Avodah Zarah 8a puts forth the talmudic hypothesis that Adam first established the tradition of fasting before the winter solstice, and rejoicing afterward, which festival later developed into the Roman Saturnalia and Kalendae.

Observation