What is the Sundial?

The World Book Encyclopaedia Volume 18 quotes that “the sundial is the oldest known device for the measurement of time.  The sundial indicates time of the day by the position of the shadow of some object (gnomon) on which the sun’s ray falls”.

 

The Background to the UNSW Millennium Sundial

On the 23rd of August 1999 Prof. Bill Kearsley, Head of the School of Surveying and Spatial Information Systems,  and Dr. George Bennett, former Head of this School,  approached the Vice Chancellor with the idea of placing a sundial on the South Tower of the Quadrangle Building, University of New South Wales Kensington Campus. 

The sundial was promoted as a tool for teaching geodesy students, as a way to locate the University of New South Wales in the global arena with other classical universities in Europe, and as a means enhancing the appearance of the Quadrangle area.  Interestingly, it transpired that the architect of the Quadrangle Building had originally designed a sundial in the circular opening on the second level, but this plan was not carried out, (mainly because this aperture was in shadow).

  Type of dial

 The dial is classified as a vertical declining sundial because it is attached to the wall that does not face north directly (in fact it bears N9°20’E of True North).  This is a typical style of sundial for walls of buildings, since it is very rare that a wall will face due North (or South).

   

 

Sundial Design Specifications

The following items were specified for the manufacture of the sundial.

·        Roman numerals for the markers (the hour line projections).

·        Gnomon, hour lines, half hour lines, numerals, and letters to be cast in bronze with a patina finish. (Note that because of the unusual size and deign of the gnomon, this created special problems in the casting, lifting and mounting stages).

·        The top edge of the gnomon to be square, and the thickness 30 mm.

·        Hour lines are made 200 mm by 40 mm                                   

·        Half hour lines are half size of the hour lines - 100 by 20 mm.

·        Size of the Roman numerals was 200 mm, but this specification changed during the manufacturing stage.  The foundry advised Dr. Bennett to increase the size of numerals by 100 millimetres, to make it easier to read them at a distance.

·        Two plaques, one with technical information, the other carrying the acknowledgements.

 

 

Pouring the 1300 deg C molten bronze for the

 gnomon, 16th August 2001

Lifting the Gnomon into position, 6th September 2001

 

 

 

Components of the Sundial

The gnomon, hour lines, half hour lines, the numerals, and the letters were made using Gunmetal, LG2.   The weight of gnomon it self weights 300 kilograms!!!  Besides all the hard work and plan of erecting sundial, the project wouldn’t have been possible without the funding of $50, 000 by the University Committee (U-Committee). 

 How to read the time

1.       Read the sun time by reading a long shadow cast by the gnomon on the wall.  Note, in the Southern Hemisphere that hours left to the 12 hour line are p.m., and the hours right to the 12 hour line a.m.

2.       To find the clock time (Eastern Standard Time or EST), adjust the dial reading by applying the correction, given by the Equation of Time, located on the left hand pillar of the Tower beneath the Sundial. This correction is caused by the combined effect of the earth’s tilt with respect to the plane of its orbit, and the earth’s elliptical orbit. It is the difference between clock time and apparent solar time. The equation of time is in the form of a bi-modal curve.  For example, on the image above  the shadow reads 10:30 a.m.  Apply the correction to the sundial time to get clock time.  If the date is assumed to be the 15 October 2001, the sun is 16 minutes ahead of clock time, so 10:30 minus 16 minutes, gives a clock time of 10:14 a.m).

Note: In daylight saving  add one hour to the EST to get Eastern Summer Time.

 

 

 

 

The Unveiling of the Sundial

 

On the 20th of November, 2001, the University Vice Chancellor, Professor John Niland, Dr. George Bennett, Prof. Bill Kearsley, the executive of the U Committee, members and former of the School and of the wider University community, ProBuild employees and media personal celebrated the birth of the Millennium Sundial (unveiling the sundial). 

 Unfortunately, it rained!!