WHAT IS A SOLSTICE ?
A solstice is a natural astronomical event during which one of the Earth’s hemispheres
is at maximum tilt away from or towards the Sun. Two solstices occur annually, around
the 21st June and the 21st December. When one hemisphere experiences a winter solstice,
the other hemisphere experiences a summer solstice.
WHY SOLSTICE ?
The word solstice means “to stand still.” The name was chosen because during a solstice the sun appears to remain stationary in its position in the sky.
The solstice in June marks the arrival of winter in the southern hemisphere. That is why in the southern hemisphere the June Solstice is known as the winter solstice or hibernal solstice. This animation by Sydney City Skywatchers fellow, astronomer Dr Nick Lomb, shows the daily motion of the Sun at the turning points of the year, the summer and winter solstices and the spring and autumn equinoxes, as seen from southern latitudes at places such as Sydney, Melbourne or Perth.
THE WINTER SOLSTICE EXPLAINED
The Earth is tilted by 23.5 degrees to the vertical. It is the tilt which determines the seasons. The winter Solstice is determined by the tilt of the southern hemisphere away from the Sun, so that the Sun makes its smallest arc across the sky taking under 12 hours (1).
For us in Australia it can occur between the 21st and 23rd of June. In 2021 the winter solstice in Australia will occur on Monday 21st June at 13:32 sharp Australian Eastern Standard Time (AEST). The latest sunrise in Sydney occurs from the 24th June for 10 days when the Sun rises at 7:21a.m. The earliest sunset is from the 5th to19th June when the Sun sets at 4:53p.m. But the shortest day is the 21st June. Find out more with this link.
In Australia evidence collected from ethno-graphic, historic, and archaeological studies indicates that Aboriginal and Torres Strait Islander people observed and noted the position of the rising and/or setting position of the Sun throughout the year. Their observations aided their survival and informed food gathering, hunting and tracking seasons. Human-made structures and the natural horizon landscape were used to mark the sun positions (2).
The Sun and seasons have been central to human survival and ritual and many Indigenous Peoples around the globe had methods of recording their observations of the solstice, and cultural activities associated with this time.
The Northern Hemisphere winter solstice was a time of celebration in ancient Europe. For example the Romans had a week-long celebration called Saturnalia during which all wars had to stop, and courts did not try criminals (3).
HOW LONG IS THE SHORTEST DAY OF THE YEAR ?
In the southern hemisphere it simply depends on how close you are to the south pole. The closer you are
to the south pole the shortest amount of daylight you will receive. On an average the southern hemisphere
will receive 9 hours of daylight during the solstice.
DID YOU KNOW?
For days before and after the winter solstice the Sun appears to stand still in the sky at its noon-time elevation.
If you stand outside at noon on the winter solstice and look at your shadow, it will be the longest shadow you will cast for the entire year.
Don’t confuse the solstice with the equinox. Both occur twice a year, but the equinox occurs when the sun is directly above the equator, and day and night are equal in length.
Lomb, 2021, Australasian Skyguide, MAAS Publishing (also diagram)
Hamacher, Leaman, Fuller, Bosun 2020, Solstice and Solar Position Observations in Australian Aboriginal and Torres Strait Island traditions, JAHH, 23.