June 21 marks the Winter solstice for the Southern hemisphere.
I love the Winter solstice, as it means that the days will now get longer for six months. It’s interesting to observe how the days get longer – if you plot the day length versus date, you get something like a nice sinusoidal curve unless you’re in the land of the midnight sun/moon.
The wikipedia entry on the Winter solstice is here: http://en.wikipedia.org/wiki/Winter_solstice
According to that article, the exact time of the Winter solstice is 12:26 Universal Time on June 21, so in Sydney it happens at 22:26. The article states that astronomically, a solstice occurs when a hemisphere has the greatest incline away from the Sun.
Aphelion, the point of farthest distance of the Earth from the Sun, occurs at 23:00 Universal Time on July 3 (thus 09:00 July 4 Sydney time).
Of course, as the Earth’s axis of rotation precesses (see http://en.wikipedia.org/wiki/Precession_of_the_equinoxes) and its orbit about the Sun gradually changes (in a cycle from elliptical to near-circular and back again), and the degree to which the tilt of the Earth’s axis changes, the solstices, equinoxes and aphelion and perihelion will all change.