(Inside Science) -- On December 21, in the Northern Hemisphere, the noontime peak of the sun's path through the sky will be the lowest of the year. The date, called the winter solstice, marks the shortest daylight hours and the longest night. It occurs because of a tilt of approximately 23.5 degrees in the Earth's axis.
The northern part of the Earth leans toward the sun in June and away from it in December. On the solstice, the angle toward or away from the sun reaches its maximum. The word solstice is derived from the Latin words "sol," meaning sun, and "sistere," meaning "to stand still." That's because the sun appears to stop at its lowest (or highest, in the case of the summer solstice) level, before reversing course.
Although the winter solstice marks the day of shortest sunlight, the coldest winter temperatures usually occur later in the season. That's because the land and water store large amount of heat from the previous months and release them slowly over time.
Many cultures around the world celebrate the winter solstice. Here's a round-up of some of the celebrations. Communities in the southern hemisphere also celebrate winter solstice, but for them the day occurs in June.
Saturnalia, Ancient Rome
Named after the Roman agricultural god Saturn, this ancient holiday lasted several days around the solstice. People feasted, exchanged gifts, and sometimes exchanged roles -- with the slaves acting like masters for a day. The festivities likely influenced the later celebrations of Christmas and New Year.
St. Lucia's Day, Scandinavia
St. Lucia's Day, sometimes called St. Lucy's Day, is celebrated on December 13, most commonly in Scandinavia. It honors a Christian saint who legend told brought supplies to Christians hiding in the Catacombs when they were persecuted by the Roman Empire.
To celebrate St. Lucia's Day, girls would dress up as St. Lucia in white dresses with red sashes and wreaths of candles on their heads. The feast day once coincided with the winter solstice, and the festival has incorporated Norse solstice traditions.
Dong Zhi, China
The Winter Solstice Festival is China is a time for families to get together and celebrate. A traditional food called tangyuan is made from glutinous rice and symbolizes reunion.
Shab-e Yalda, Iran
In Iran, families celebrate the winter solstice by gathering to read poetry, eat special foods like nuts and pomegranates, and stay awake long into the night.
Inti Raymi, Peru
Celebrated in June, Inti Raymi honors the Incan Sun god. Spanish conquistadors banned the holiday, which included animal and possibly human sacrifices. It was brought back in the 20th century with mock sacrifices.