The axial tilt of Earth and gyroscopic effects of its daily rotation mean that the two opposite points in the sky to which the Earth's axis of rotation points (axial precession) change very slowly (at the current rate it would take just under 26,000 years to make a complete circle). As the Earth follows its orbit around the Sun, the polar hemisphere that faced away from the Sun, experiencing winter, will, in half a year, face towards the Sun and experience summer. This is because the two hemispheres face opposite directions along Earth's axis, and so as one polar hemisphere experiences winter, the other experiences summer.
More evident from high latitudes, a hemisphere's winter solstice occurs on the day with the shortest period of daylight and longest night of the year, when the sun's daily maximum elevation in the sky is at its lowest. Although the winter solstice itself lasts only a moment in time, the term sometimes refers to the day on which it occurs. Other names are "midwinter", the "extreme of winter" (Dongzhi), or the "shortest day". In some cultures it is seen as the middle of winter, while in others it is seen as the beginning of winter. In meteorology, winter in the Northern Hemisphere spans the entire period of December through February. The seasonal significance of the winter solstice is in the reversal of the gradual lengthening of nights and shortening hours of daylight during the day. The earliest sunset and latest sunrise dates differ from winter solstice, however, and these depend on latitude, due to the variation in the solar day throughout the year caused by the Earth's elliptical orbit (see earliest and latest sunrise and sunset).
Worldwide, interpretation of the event has varied across cultures, but many have held a recognition of rebirth, involving holidays, festivals, gatherings, rituals or other celebrations around that time.
The solstice may have been a special moment of the annual cycle for some cultures even during neolithic times. Astronomical events were often used to guide activities such as the mating of animals, the sowing of crops and the monitoring of winter reserves of food. Many cultural mythologies and traditions are derived from this. This is attested by physical remains in the layouts of late Neolithic and Bronze Age archaeological sites, such as Stonehenge in England and Newgrange in Ireland. The primary axes of both of these monuments seem to have been carefully aligned on a sight-line pointing to the winter solstice sunrise (Newgrange) and the winter solstice sunset (Stonehenge). It is significant that at Stonehenge the Great Trilithon was oriented outwards from the middle of the monument, i.e. its smooth flat face was turned towards the midwinter Sun. The winter solstice was immensely important because the people were economically dependent on monitoring the progress of the seasons. Starvation was common during the first months of the winter, January to April (northern hemisphere) or July to October (southern hemisphere), also known as "the famine months". In temperate climates, the midwinter festival was the last feast celebration, before deep winter began. Most cattle were slaughtered so they would not have to be fed during the winter, so it was almost the only time of year when a plentiful supply of fresh meat was available. The majority of wine and beer made during the year was finally fermented and ready for drinking at this time. The concentration of the observances were not always on the day commencing at midnight or at dawn, but at the beginning of the pagan day, which in many cultures fell on the previous eve.
Because the event was seen as the reversal of the Sun's ebbing presence in the sky, concepts of the birth or rebirth of sun gods have been common and, in cultures which used cyclic calendars based on the winter solstice, the "year as reborn" was celebrated with reference to life-death-rebirth deities or "new beginnings" such as Hogmanay's redding, a New Year cleaning tradition. Also "reversal" is yet another frequent theme, as in Saturnalia's slave and master reversals.
Iranian people celebrate the night of the Northern Hemisphere's winter solstice as, "Yalda night", which known to be the "longest and darkest night of the year". In this night all the family gather together, usually at the house of the oldest, and celebrate it by eating, drinking and reading poems (esp. Hafez). Nuts, pomegranates and watermelons are particularly served during this festival.
The pagan Scandinavian and Germanic people of northern Europe celebrated a twelve-day "midwinter" (winter solstice) holiday called Yule (also called Jul, Julblot, jólablót, midvinterblot, julofferfest). Many modern Christmas traditions, such as the Christmas tree, the Christmas wreath, the Yule log, and others, are direct descendents of Yule customs. Scandinavians still call Yule "Jul". In English, the word "Yule" is often used in combination with the season "yuletide" a usage first recorded in 900. It is believed that the celebration of this day was a worship of these peculiar days, interpreted as the reawakening of nature. The Yule (Jul) particular god was Jólner, which is one of Odin's many names.