Summer and Winter Solstice

The summer solstice occurs once a year in December when the Sun's track across the Australian sky reaches its highest point. It is the day that has the most daylight hours of any in the year. The summer solstice usually occurs on 21 December, but can occur between 20 and 22 December. The winter solstice is the day of the year that has the least daylight hours of any in the year and usually occurs on 21 June but can occur between 20 and 22 June.

Sunrise, sunset and daylight hours

An interesting idiosyncrasy relating to the summer solstice is that it does not feature the day with the earliest sunrise and latest sunset as is commonly expected. Similarly, on the winter solstice, the sunrise is not the latest and the sunset is not the earliest. However, this day does have the least amount of daylight hours.

Because the path of the Earth around the Sun is an ellipse, not a circle, and because the Earth is off-centre on its axis, these combined phenomena can create up to several minutes difference between solar and mean time. Around the date of summer solstice, these effects make the Sun appear to move slightly slower than expected when measured by a watch or clock. As a result, the earliest sunrise occurs before the date of the summer solstice, and the latest sunset happens after the summer solstice. For the same reasons, around the winter solstice, the time of sunrise continues to get later in the days after the solstice.