In astronomy, the winter solstice is the moment when the earth is in a point of its orbit at which the northern or southern hemisphere is most inclined away from the sun. This causes the sun to appear at its farthest below the celestial equator when viewed from earth. Solstice is a Latin borrowing and means "sun stand", referring to the appearance that the sun's noontime elevation change stops its progress, either northerly or southerly.
The date of the winter solstice is the date with the shortest day and the longest night of the year. In the northern hemisphere, this date usually falls on December 21/December 22, while it falls on June 21/June 22 in the southern hemisphere. These dates are also the dates of the summer solstice in the opposing hemisphere. At the summer solstice, the hemisphere is inclined towards the sun, and it appears to be at its farthest above the celestial equator.
In some reckonings, the winter solstice is the first day of winter. In the Chinese calendar, for example, the winter solstice is called dong zhi (winter's arrival) and is regarded in certain Chinese areas as an equally, if not more, important Jie Chia compared to the Chinese New Year.
In other reckonings, the winter solstice is midwinter . In Ireland, the solstices and equinoxes all occur at about midpoint in each season. For example, winter begins on November 1, and ends on January 31.
The winter solstice is the time when the Germanic festival of Yule was celebrated; it is celebrated today as a Neopagan Sabbat. Many cultures celebrate or celebrated a holiday near (within a few days) the winter solstice; examples of these include Yalda, Saturnalia, Christmas, Hannukah, Festivus, Kwanzaa, and HumanLight. In her fiction, Ursula K. Le Guin calls the solstice celebration "The Festival of Sunreturn".
- The seasons begin at the time of the solstice or equinox http://www.badastronomy.com/bad/misc/badseasons.html (from the Bad Astronomer)
- Solstice does not signal season's start? http://www.straightdope.com/classics/a1_170b.html (from The Straight Dope)
- Solstice Dates and Times http://www.islandnet.com/~see/weather/almanac/seasondate.htm