Millennium Sundial Explained
By Bill Kearsley
Many people observe the sundial on the tower of the Quadrangle
building and have wondered how to read the time from this object
of curiosity. As the person responsible for its existence, I feel
I should give some explanation for it, especially why its time
does not always agree exactly with the time shown on our watches.
The sundial tells the local solar time. We read this time by
measuring the shadow of the straight edge of the gnomon (the long
vertical triangular column) against the sundial face. For example,
the time on the sundial in the photograph is 12:10 pm. This is
quite close to Eastern Standard Time (EST), but may differ from
it depending on the season. The difference is described in the
Equations of Time plaque mounted on the Northern Column of the
Quadrangle Tower.
For example, if we were reading the sundial on 20 July, we would
need to add six minutes to our sundial time to bring it to EST.
The Eastern Standard Time from our sundial reading would therefore
be 12:10 plus 6, or 12:16 pm.
A further refinement is needed if we read the sundial during
Daylight Saving, or Eastern Australian Summer Time, when clocks
are one hour ahead of EST. For example, if the sundial reading
in the photograph had been made on 15 January, EST would be 12:10
plus ten minutes, or 12:20 pm. To bring this to Daylight Saving
or Eastern Australian Summer Time, we would now add an hour, and
the time (as read by our watches at that time of the year) would
actually be 13:20 pm.
The sundial is appropriate to the times. It was erected and unveiled
in 2001, the start of the third millennium. For this reason we
proposed that the sundial be called the UNSW Millennium Sundial.
So, what is a sundial? The sundial is a device that indicates
the time of day by the position of the sunÕs shadow cast on a
graduated surface. It is one of the earliest of mankindÕs inventions
to measure time. Sundials were very common in Roman times and
there are many examples of them in the archaeological museums
of the sites of ancient towns, such as Pompeii. Their construction
flourished during the Renaissance, and there are many beautiful
examples of them to be seen in many of the early churches and
universities of Europe, such as Oxford, Cambridge, Paris and Uppsala
in Sweden.
The sundial was a very common sight in the early universities,
as the sciences and the classical arts studied in those institutions
came together nicely in the sundial; the sciences, because the
knowledge of astronomy and the use of mathematics enabled the
precise computation and location of the hour lines on the dial;
the arts, because the form lent itself to the creative design,
which often alluded to classical scholarship and learning.
The School of Surveying and Spatial Information Systems designed
and constructed the Millennium Sundial on the south tower of the
Quadrangle building. It is probably the largest vertically mounted
sundial in the world, as its size (the gnomon is two metres long)
and weight (more than 300 kg) presented special problems for mounting.
Of all the precincts on the Kensington Campus, the Quadrangle
area Š which echoes the cloisters of the older European universities
Š is the most appropriate. By locating it high on the buildingÕs
fourth level, the sundial catches the early morning and late afternoon
sun. Its construction received enthusiastic support both from
the U Committee, which provided funding, and from the then Vice-Chancellor
Professor John Niland, and had special oversight from Paul Turner
of Facilities.
It is a useful teaching tool in the study of geodesy and positioning.
Astronomy was one of the principal studies in medieval universities,
where the study of the sun and stars led to our understanding
of the nature of the solar system and of EarthÕs motions in space.
Its use in navigation and positioning as the means of establishing
our location on the globe has only been superseded by the advent
of satellite positioning. Nevertheless, an understanding of the
various motions of the Earth in space is still fundamental to
the study of global positioning.
The sundial will provide a means whereby we observe not only
the daily passage of the sun across the sky but also the variations
in the sunÕs elevation in the sky with the passing of the seasons.
Dr AHW (Bill) Kearsley is Visiting Associate Professor and
former head of the School of Surveying and Spatial Information
Systems in the Faculty of Engineering. More information about
the design and construction of the sundial can be found on the
School of Surveying and SIS website, at http://www.gmat.unsw.edu.au/currentstudents/ug/projects/yj/sundial.htm.
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