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You will find the Sundial of Human Involvement just off Caley Drive - stop at the sign and walk up the path on the right hand side of the road to Sundial Hill, located near a saddle of Mount Annan. From here there is a spectacular 360 degree view of the surrounding countryside. On a clear day you will see the city of Sydney to the north-east and the Blue Mountains to the west
A rare type of sundial
The Sundial of Human Involvement is a rare type of sundial that uses a person’s body to cast a shadow onto hour markers and to tell the time. The position of the person is adjusted throughout the year following a figure of eight pathway, or analemma - so this type of sundial is known as an analemmatic sundial.
Telling the time
Follow the instructions on the nearby bronze plate. When your feet are on the correct date, clock time is given by the position of your shadow, providing you are tall enough - you might have to raise your hands above your head to become a bit taller! Check the time on the conventional horizontal sundial (accurate to within 1 or 2 minutes) on your right, but remember to follow all the instructions correctly!
How accurate is the Sundial of Human Involvement?
The simple method of telling the time using the Sundial of Human Involvement does not give precise clock time throughout the whole year. However, the small errors lie within the width of the shadow and occur in the early morning and late afternoon at times of the year corresponding to the maximum and minimum of the equation of time (see below). The novelty value of being able to read clock time directly from a sundial well compensates for the slight mathematical imperfections introduced!
The hour markers
The analemma plate
Solar time and clock time
The Sundial of Human Involvement incorporates the effects of longitude into the position of the basalt crystals used as hour markers, while the equation of time corrections are built into the central analemma.
Design of the Mount Annan sundial
Other analemmatic sundials
Making your own analemma
Instead of a hole you can use a mirror about 50 mm square (or round) located on a window sill to produce analemmas on the ceiling and walls of a room.
Layout of the sundial
The Sundial of Human Involvement consists of an elliptical ring of basalt crystals, which represent the hour markers, with a major axis of about 5 meters and a minor axis of 3 meters. Each hour marker has a number carved in it. Inside the ellipse, and located along the north-south line, is an analemma with dates marked on it at fortnightly intervals around the circumference.
A gift to the Garden