Because the Earth's axis is tilted, the length of a day changes during the course of a year, with the longest stretch of daylight in midsummer, and the shortest day falling in midwinter.
It's based on Earth's position in relation to the sun and the 21st is when we'll see the winter solstice, the shortest day of the year when astronomical winter begins.
It falls at the midpoint between the winter solstice and the spring or vernal equinox, making it the ideal time to consider when springtime might finally come.
And although the rituals of Yuletide and the winter solstice have mostly fallen out of practice due to the rise in popularity of Christianity in Europe, many of the traditions associated with the period are still around.
It is very difficult to obtain, as when the fruit ripens, on a full-moon night around the winter solstice, the fruit explodes as a mechanism to spread its seeds.
According to legend, during the midwinter feast 2,500 years ago, the King of Wu was disgusted with all kinds of costly foods and wanted to eat something different.
Certain stones in the ancient circle line up with the midsummer sunrise and the winter solstice sunset, marking the longest and shortest days of the year.
As with many modern celebrations, ancient festivals observing the winter solstice merged with newer traditions to create the holiday season as we know it today.
China has developed an unique festive food culture throughout the years. Eating dumplings is a common folk custom for many Chinese on the day of winter solstice, especially those living in the north.