The December solstice can be on December 20, 21, 22, or 23.
The North Pole is tilted furthest from the Sun.
It is the winter solstice in the Northern Hemisphere, where it is the darkest day of the year.
In the Southern Hemisphere, it is the summer solstice and the longest day of the year.
The winter solstice happens every year when the Sun reaches its most southerly declination of -23.5 degrees. In other words, it is when the North Pole is tilted farthest away from the Sun, delivering the fewest hours of sunlight of the year.
The Sun is directly overhead of the Tropic of Capricorn in the Southern Hemisphere during the December solstice and is closer to the horizon than at any other time in the year.
The day after the winter solstice marks the beginning of lengthening days, leading up to the summer solstice in June.
In the Southern Hemisphere, the opposite is true. Dawn comes early, and dusk comes late. The sun is high and the shortest noontime shadow of the year happens there. In the Southern Hemisphere, people will experience their longest day and shortest night.
Does the winter solstice always occur on December 21st?
While it more often than not falls on December 21st, the exact time of the solstice varies each year. In the Northern hemisphere, the winter solstice is the shortest day of the year, because it is tilted away from the sun, and receives the least amount of sunlight on that day.
However, the earliest sunset does not occur on the solstice, because of the slight discrepancy between ‘solar time’ and the clocks we use.
The shortest day of the year often falls on December 21st, but 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.
The solstice can happen on December 20, 21, 22 or 23, through December 20 or 23 solstices are rare. The last December 23 solstice was in 1903 and will not happen again until 2303.
The term ‘solstice’ derives from the Latin word ‘solstitium’, meaning ‘Sun standing still’. On this day the Sun seems to stand still at the Tropic of Capricorn and then reverses its direction as it reaches its southernmost position as seen from the Earth. Some prefer the more Teutonic term ‘sunturn’ to describe the event.