Hundreds of people are expected at Stonehenge in Wiltshire to see the sun rise on the winter solstice.
The solstice annually attracts an eclectic mix - Druids, hippies, sun worshippers and those who are curious to experience the ancient festival.
Members of the public will also visit the site, near Salisbury Plain, Wiltshire, hoping to see the sun rise through the ancient stones.
The shortest day of the year often falls on December 21, but this year the druid and pagan community will mark the first day of winter on Wednesday because the modern calendar of 365 days a year - with an extra day every four years - does not correspond exactly to the solar year of 365.2422 days.
Peter Carson of English Heritage said: "We are delighted to offer people a warm welcome to Stonehenge this Winter Solstice.
"Over the years, the event has grown from a handful of people to a celebration enjoyed by a couple of thousand of people. We work very closely with the Druid and Pagan community to ensure that the event is a success."
The word solstice comes from the Latin phrase for "sun stands still". During the winter solstice the sun is closer to the horizon than at any other time during the year, meaning shorter days and longer nights.
The day after the winter solstice marks the beginning of lengthening days leading up to the summer solstice in June. The sun's passage through the sky appears to become stationary, with the sun seeming to rise and set in the same two places for several days.
Then the arc begins growing longer and higher in the sky, reaching its peak at the summer solstice. The solstices happen twice a year because the Earth is tilted by 23.5 degrees as it orbits the sun. Since ancient times people have marked the winter and summer solstices. The stones at Stonehenge are aligned with the sunlight on both the summer and winter solstice.
These times told prehistoric farmers that harvest was coming or that the shortest day of winter had past. Recent excavations of animal bones at the site suggest that huge midwinter feasts were held at Stonehenge with cattle moved there to be slaughtered for the solstice celebrations.