The ancient Celts celebrated the summer and winter solstice as the time when the day length started to change. The December solstice occurs at 02:59 AEDT on December 22. At this time the South Pole of the earth will be tilted toward the Sun. The Sun will have reached its southernmost position in the sky and will be directly over the Tropic of Capricorn at 23.44 degrees south latitude. This is the first day of winter (winter solstice) in the Northern Hemisphere and the first day of astronomical summer (summer solstice) in some countries in the Southern Hemisphere
If you have been able to regularly watch the sunrise or sunset (a bit difficult of late in the eastern states with all the rain and cloud) you may have noticed that it rises and sets in a different place each day relative to the horizon. Due to a combination of the Earth’s tilt and orbit, over the course of a year the place against the horizon where the Sun rises and sets moves north, and then south, and back again, and the days where it reaches its maximum and turns around are the solstices. The word ‘solstice’ comes from ancient Latin – sol: sun, sistere: stand still.
On 22 December the Sun has reached its most northern location. Following this, it will then appear to move south a little more each day. It can be a fun little project over the next few months to make a note of where the Sun sets. You don’t have to do it every day, but try it maybe once a week, note where the Sun has set against the horizon and watch it move week after week. You should catch the last of its northern motion before the turning point on the 21st and the subsequent southern motion.
The December solstice is also the day of the year with the most amount of daylight for those in the southern hemisphere, and from here on out the days will get shorter. Note that this doesn’t mean that sunset will be earlier – in fact, it’s still getting later as summer progresses, but the later sunrises each day will start to shave time off the length of the day, making this a maximum length day.