2013 Dec 21
21 December will mark midwinter in the northern hemisphere, and midsummer in the southern hemisphere.
On this day, the Sun will reach its most southerly point in the sky, as it tracks along its annual path through the constellations – the line of the ecliptic of zodiac.
As a result, the northern hemisphere will experience its shortest day and its longest night. Conversely, the southern hemisphere will experience its longest day and its shortest night.
According to the astronomical definitions of the seasons, this moment marks the beginning of winter in the northern hemisphere and of summer in the southern hemisphere.
At the December solstice, the Sun appears overhead at noon when observed from locations on the tropic of Capricorn, at a latitude 23.5°S.