Tuesday 21 June was the shortest day of the year, or the winter solstice.
More correctly, it was the day on which the solstice fell, at 4:46pm AEST.
The word ‘solstice’ means ‘sun stands still.’ Although the Sun never stops moving across the sky, it does stop moving in a north-south direction. The winter solstice is the precise moment at which the Sun reaches its northernmost point and then starts moving south again.
Of course, the Sun itself is not really moving north and south. Its apparent motion is a result of the tilt in the Earth’s axis and the motion of the Earth around it. On our winter solstice, the tilt points directly away from the Sun, which sits lowest in the sky, and sunlight is the most spread out across the ground.
The day on which the solstice falls is the shortest day of the year, but not the day with the latest sunrise or the earliest sunset.
This is because sun time does not keep exactly in step with clock time. Around the winter solstice, clock time is getting ahead of sun time, so both sunrise and sunset get later relative to the clock. The longer day will not be enough to offset this shift for about two and a half weeks, so sunrise will keep getting later until then. Similarly, the earliest sunset happened about two and a half weeks ago.
Nor is the solstice the coldest day of the year. Although the ground will start receiving more sunlight, it is not enough to actually start warming it for another month. Until then the land and sea will continue losing some of their stored heat.