Thursday is the winter solstice -- the shortest day of 2017.
December 21 also marks the first day of astronomical winter -- although meteorological winter began December 1. In the Northern Hemisphere, where most of the world's population lives, the winter solstice marks the shortest day of the year and the longest night.
The good news for sunlight seeking Northern Hemisphere natives is that the days start getting longer beginning Friday -- and they can start counting down to spring.
It's the shortest day of the year because, during the winter solstice, the Northern Hemisphere is tilted 23.5 degrees away from the sun and the sun's position is at its most southerly point, directly over the Tropic of Capricorn -- right across the middle of Australia.
With the sun positioned so far to the south, the tilt of the Earth leaves the Arctic Circle entirely in the dark. In the Southern Hemisphere, the opposite is true. They experience their longest day and shortest night of the year.
The Southern Hemisphere refers to this event as the December Solstice because seasonally it signals the beginning of their summer.
Historically the solstice has been celebrated by people around the globe. At Stonehenge in England, many gather to watch the sunrise to signify the start of longer days ahead. In ancient times the Incas would celebrate the solstice at the Temple of the Sun in Machu Picchu, Peru.
- The next summer solstice will take place on June 21, 2018.
- Summer solstice in the Northern Hemisphere occurs on June 20, 21 or 22, when the sun reaches its most northerly point, directly overhead at the Tropic of Cancer (23 degrees 27 minutes north latitude). The summer solstice is the longest day of the year and marks the beginning of summer.
- Winter solstice in the Northern Hemisphere occurs on December 21 or 22, when the sun appears at its most southerly position,directly overhead at the Tropic of Capricorn (23 degrees 27 minutes south latitude). The winter solstice is the shortest day of the year and marks the beginning of winter. It is the exact opposite in the Southern Hemisphere.
- A solstice is different from an equinox, the two times each year when the sun is directly above the Earth's equator and day and night are of equal length. Equinoxes mark the beginning of spring (March) and fall (September).
- Solstice loosely translated in Latin is "sun stands still". For several days before and after each solstice the sun appears to stand still in the sky, i.e., its noontime elevation does not seem to change from day to day.
- Historically, the solstice has been celebrated by numerous cultures around the world. Thousands of people annually celebrate the summer solstice at Stonehenge in Wiltshire, England.
- At sunrise at Stonehenge on the longest day of the year, the rising sun appears behind one of the main stones, creating the illusion that the sun is balancing on the stone.
- Stonehenge was closed for 16 years after rioting broke out between police and revelers for several years at solstice gatherings. The site was re-opened to the public on the solstice in 2000.