On the northern winter solstice (around the 21st December each year), the Sun reaches its most southerly declination of -23.5 degrees.

This means that for an observer on the Tropic of Capricorn in the Southern Hemisphere, the Sun will be directly overhead, and the northern winter solstice marks the longest day of the year (most hours of daylight). On the contrary, for an observer in the Northern Hemisphere, the northern winter solstice marks the shortest day of the year (least hours of daylight). The southern winter solstice occurs 6 months later, around 21 June.