VERTICAL SUNDIALS

Although relatively rare in Australia, vertical sundials are quite common in Europe They are often placed on the walls of public buildings and churches where they can be widely seen and admired yet remain out of harm’s way.

 

For many centuries these public sundials were the only way that most people could tell the time. Some towns and cities became quite famous because of their grand vertical sundials.

 

The shadow casting gnomon of a vertical sundial is often made from a rod, rather than the solid structure used for a horizontal sundial. Solar time is told by reading the position of the centre of the shadow cast  by the rod-gnomon.

 

Vertical sundials need to be individually designed for each wall, since the hour angles depend critically on the orientation of the wall with respect to a true East-West line. In addition, the hour angles are dependent on the latitude and longitude of the sundial's location.

 

The first illustration shows a  Celtic Cross vertical sundial made from stainless steel, on the wall of 'Bishops Court', the Anglican Archbishop’s residence in Adelaide, South Australia. Notice that the morning and afternoon hour lines are asymmetric - this is because the wall does not face true North but declines 13 degrees towards the West.

The cross is about 3 metres tall. The stainless steel has been chemically treated to prevent dazzling reflections.

Vertical sundial at 'Bishops Court' in Adelaide.

The second illustration shows a vertical wall sundial made from slate, located in a private residence in New Zealand. It is about 1.2 metres tall.

 

Not only does it tell the time - it also indicates the date. The shadow cast by the rod gnomon tells solar time throughout each day, while the shadow cast by the small spherical ball (the ‘nodus’) attached to the gnomon rod  travels along the respective date lines on 3 important days throughout the year, namely, midsummer, midwinter and equinox. Specific date lines can be computed and marked to suit your special needs.

 

The Sun cannot shine on a vertical sundial for more than 12 hours in any day because the sun’s azimuth passes behind the plane of the wall outside these hours. There is thus no scientific value in marking more than 12 hours on any vertical sundial. However, purely for appearance, more hours than are strictly necessary are often marked on the dialplate.

Vertical sundial at 'Stone Farm' near Otago in New Zealand.

Substrates of metal, stone or wood can be used. Our techniques include metal casting and fabrication, laser cutting, waterjet cutting, sandblasting and painting. For the ultimate in presentation gifts, you could consider a stained glass window sundial such as described below. 

 

Christian Brothers College, Adelaide

Tower sundial at Ellenbrook, near Perth

Stained glass window sundial at Scotch College, Melbourne

The Ellenbrook sundial is fabricated from welded steel bars and is 2 metres square. The metal assembly was mounted directly onto the stone tower.

 

The wall sundial at Christian Brothers College is 1.2 metres square and includes Date Lines for Solstices and Equinoxes. It was cut from a stainless steel sheet using a high pressure jet of water then mounted on a weatherproof backing board before attachment to the brick wall.

The stained glass window sundial at Scotch College is a spectacular variation. Here the traditionally shaped solid triangular gnomon sits outside the building and the hour lines, numbers, sundial furniture and gnomon shadow are arranged to be read from inside the building. Solar time is read from the outside edge of the gnomon shadow, which is the left edge of the shadow in the morning, and the right edge of the shadow in the afternoon.

When vertical sundials are designed in matching pairs to fit on the corner of a building, the rod gnomons are parallel but the hour markings are quite different. These corner sundials look quite dramatic.

 

Do not use a magnetic compass to measure the wall orientation. True North and Magnetic North can be appreciably different, as explained in Chapter II of Our Book. A precise method for measuring the deviation of a wall from a true East-West line is explained on page 77 of this book.

Prices depend on size, complexity and materials of construction.

Contact us to discuss your requirements.