UNUSUAL SUNDIALS

Projection sundial at the Australian Arid Lands Botanic Garden, Port Augusta

The shadow cast by one fixed surface onto any other fixed surface can be used produce a Projection sundial which tells the time and the date in a variety of ways. This type of sundial is ideal for a park, large garden or public place.

 

The Projection sundial shown below at the Australian Arid Lands Botanic Garden at Port Augusta in South Australia indicates both clock time and the date. A stainless steel plate, mounted at the latitude angle, faces true North (in the Southern hemisphere). Sunlight shines through a small circular hole in the plate (the nodus) and produces a bright patch of light on a horizontal surface which has date lines on it and a family of analemmas ('figures of 8') which are marked to indicate the date at specific times. As the sun’s position varies throughout the year, the projected bright spot of light moves around a figure of 8 path for any particular fixed clock hour.

Floor area is about  6 x 5 metres.

projection sundial Port Augusta
projection sundial detail

Projection sundial at the Port Augusta Arid Lands Botanic Garden

Here, the bright patch of light indicates that clock time is 9am on 19 December

projection sundial nodus
projection sundial plan

Diagrams illustrating the nodus table and floor plan of the Port Augusta projection sundial

Noon Mark Meridian at Whyalla, South Australia

 

A Noon Mark is the simplest example of a Projection Sundial, featuring a North-South line to indicate solar noon and an analemma to indicate clock noon. The bright spot of light shining through a hole is equivalent to the end of a solid shadow cast by a vertical stick, but more interesting and better defined. 

meridian sundial nodus
noon mark sundial

 

During installation of the Noon mark meridian

The nodus plate and meridian layout

When the bright patch of light crosses the analemma curve marked in blue on the horizontal surface, the Noon Mark sundial indicates 12 Noon Central Standard Time (or 1pm Daylight Saving Time). You can read the date using the months marked on the horizontal plate.  

 

When the bright patch of light crosses the straight line marked in black, the Noon Mark sundial indicates Solar Noon, which occurs when the sun is due North and at its maximum altitude for that day. This black line runs in a North-South direction.

clock noon sundial

1pm Central Standard Time on 27 January

solar noon sundial

Solar Noon on 27 January

Polar sundial on the Mornington Peninula, Victoria

An Astronomical Society wanted an accurate and simple demonstration to show the variation of the sun's declination angle throughout the year (declination is discussed in Our Book). 

 

Sundials Australia created this polar sundial where the dialplate cast in gunmetal bronze is inclined at the latitude angleThe nodus is a circular annulus attached to a rotating pin that swivels to allow a bright spot of light to strike the dialplate. This enables an image of the sun to be projected on to the dialplate This sundial tells the time and the date and shows the variation in declination between plus 23.5 degrees (mid summer) and minus 23.5 degrees (mid winter).

polar sundial astromonomical

Polar sundial with a rotating nodus.

The representative sunbeam shown here indicates that solar time is 8am on either 8 February or 3 November.

Pillar sundial at Arkaroola Wilderness Sanctuary, South Australia

Most sundials tell the time using the direction of the sun's shadow (azimuth) cast by a gnomon inclined at the latitude angle of your location.

 

Pillar sundial tells time by measuring the altitude of the sun, or rather, the length of the shadow cast by the gnomon. The gnomon is a horizontal rod which can rotate about a vertical column on which are inscribed a series of spiral curves representing the sun's altitude at different times of the year. The column is marked with vertical lines representing the subdivision of the year into 12 months. The gnomon is set at the position corresponding to today's date and then pointed towards the sun. The whole assembly is turned until the gnomon shadow is exactly vertical. The length of the shadow indicates the time as shown by the various spiral curves. Interpolation between the curves enables more precise time-telling to be achieved.

 

In this example, two steel drums have been welded together then mounted on a bearing so that both the gnomon and the pillar can be rotated independantly. The appropriate time and date lines were painted on, so that if you know the date you can then tell the time.

pillar sundial arkaroola

Pillar sundial at Arkaroola.

In Photo A, the short winter shadow on 20 June tells us that solar time is 11am (or 1pm).

In Photo B, the long summer shadow on 15 November indicates solar noon. 

This is an ideal and safe instrument for young people to learn about the daily and seasonal variations in the sun's position and its direct connection to the date and the time. 

Sundials Australia can create any variety of sundial type. 

Contact us to discuss your specific wishes.