Winter solstice

Winter solstice
Lawrence Hall of Science visitors observe sunset on the day of the winter solstice using the Sunstones II
Also called	Midwinter, Yule, the Longest Night
Observed by	Various cultures, ancient and modern
Type	Cultural, seasonal, astronomical
Significance	Astronomically marks the beginning of shortening nights and lengthening days
Celebrations	Festivals, spending time with loved ones, feasting, singing, dancing, fires
Date	Between December 21 and December 22 (NH) Between June 20 and June 21 (SH)
Frequency	Annual
Related to	Winter festivals and the solstice

Winter solstice in Northern Hemisphere over Asia

Winter solstice is an astronomical phenomenon which marks the shortest day and the longest night of the year. Winter solstice occurs for the Northern Hemisphere in December and for the Southern Hemisphere in June.

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 change very slowly (making a complete circle approximately every 26,000 years). 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 shortest day and longest night of the year, when the sun's daily maximum elevation in the sky is at its lowest.^[1] The winter solstice itself lasts only a moment in time, so other terms are used for the day on which it occurs, such as "midwinter", or the "shortest day". It is often considered the "extreme of winter" (Dongzhi in the Chinese calendar), although 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 of days. 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 from culture to culture, but many cultures have held a recognition of rebirth, involving holidays, festivals, gatherings, rituals or other celebrations around that time.^[2]

History and cultural significance

Japanese Sun goddess Amaterasu emerging from a cave.

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 erected outwards from the centre of the monument, i.e. its smooth flat face was turned towards the midwinter Sun.^[3] 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.^[4] 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.

The Christmas carol In The Bleak Midwinter refers to the Winter solstice in its title.

Observances

Neolithic site of Goseck circle. The yellow lines are the direction the Sun rises and sets at winter solstice.

Sunrise at Stonehenge on the Winter Solstice

Although the instant of the solstice can be calculated,^[5] direct observation of the solstice by amateurs is impossible because the sun moves too slowly or appears to stand still (the meaning of "solstice"). However, by use of astronomical data tracking, the precise timing of its occurrence is now public knowledge. One cannot directly detect the precise instant of the solstice (by definition, one cannot observe that an object has stopped moving until one later observes that it has not moved further from the preceding spot, or that it has moved in the opposite direction). Further, to be precise to a single day, one must be able to observe a change in azimuth or elevation less than or equal to about 1/60 of the angular diameter of the sun. Observing that it occurred within a two-day period is easier, requiring an observation precision of only about 1/16 of the angular diameter of the sun. Thus, many observations are of the day of the solstice rather than the instant. This is often done by observing the sunrise and sunset or using an astronomically aligned instrument that allows a ray of light to be cast on a certain point around that time. Before the scientific revolution, many forms of observances, astronomical, symbolic or ritualistic, had evolved according to the beliefs of various cultures, many of which are still practiced today.

See also

References

External links

• Table of times/dates from 1600-2400