Monday, 2 January 2012

Sourcing and Installing Sundials

We were delighted to receive a sundial as a gift for Christmas. We’d been keen on having for quite a while as both a tool to use for telling the time naturally and as a garden feature.

Our thinking was that a sundial would be a simple process to source and install, but not so as it turns out. We contacted Larry Varley who lives in Victoria and makes both sundials and weathervanes ( for some answers to a few questions we had. Some of the comments that follow come mainly from the conversation we had with Larry.

The two components of a sundial are the sundial itself (or base-plate) and the 'style' which is the thing that stands up from the sundial and casts the shadow.

Most sundials are made in India. These are not expensive, but the catch is that they most are made for the northern hemisphere. If these are installed in Australia they are useless aside from midday for telling the time.

The sundial should be installed on a level surface in a place where it will be in direct sunlight for most of the day. In our case, we decided to relocate and use the old base 'milk and cream separator' base that the Causer family installed when they lived here during the period 1950-1965. We’ve positioned the base to the north of the house near the verandah. It will be a great location for it now that the large tree that used to be near the car shed has been removed. This photo shows the base with the sundial sitting on top of it.

The style needs to also be pointing toward true north. It is a simple process to loosen the screw on the underside of the sundial, turn the style to get it pointing to the ‘north’ indicator on the sundial, and retighten the screw.

The sundial needs to be oriented to ‘true’ (rather than magnetic) north. Here’s a few website links that give some important explanations:

2. Geoscience Australia – Calculator - Australian Geomagnetic Reference Field Values -

Using point 2 above it turns out the variation we need to use is 11.357 degrees.


For absolute accuracy the angle of the style should be equal to the latitude of the location. We checked ours and found the angle to be 37.5 degrees, meaning that it has been manufactured for use on latitudes about the same as the city of Melbourne. We are located about 33.5 degrees south so won’t get absolutely accurate time unless we purchase a new style. It may well be that the gradations on the sundial vary according to latitude as well.


As a general rule with sundials it is unlikely that the time on one’s watch will align precisely with the time on the dial. This is because of the way time zones are in place globally. Our area of Australia is such that we fall within Australian Eastern Standard Time (AEST) during the cooler period of the year and Australian Eastern Daylight Time (AEDT) during the warmer part of the year. AEST is set at 10 hours ahead of Coordinated Universal Time (UTC) and AEDT is 11 hours ahead of UTC. It gets tricky to figure out what the time should be on the sundial because each time zone applies to a range of degrees of longitude simultaneously i.e. each location that is within the same time zone regardless of its specific longitude uses the same time while the position of the sun relative to the sundial changes constantly.


It is something of a brain-teaser exercise to work through the various aspects of how time is calculated. Here are some bits and pieces that have come out of our research (NB: Some figures are approximate only):

·         The circumference of the Earth is 40,075.16 km

·         A full circle is divided into 360 degrees

·         It takes 24 hours for the Earth to do a full revolution

·         During each hour the Earth rotates 15 degrees

·         Given there are 60 minutes in 1 hour the Earth rotates through 1 degree every 4 minutes

·         The speed of the surface of the Earth based on circumference and daily revolving calculates at approximately 1,670 km / hour

·         We are located 148 degrees east of Greenwich

·         We are thus technically 9 hours 52 minutes ahead of the true time at Greenwich at any moment in time

·         The rotation of the Earth is slowly declining.


What we’ve concluded from all of the above is that understanding the various aspects of sundials is far from simple. The moral of the story also is that if you want your sundial to be very accurate then you should buy one made locally from someone who has the ability to customise components to suit your location.

1 comment:

Phillip Diprose said...

We sent a link to this article to Larry Varley who kindly responded with some additional information.
It turns out that the sundial we have was made by Arrow Engraving (now Arrow Bronze) in Melbourne. By the look of things they no longer make sundials as their main business is making funeral and general plaques.
There is no point in us changing the angle of the style as the hour lines on the sundial are a function of the angle of the style.
It is not clear whether the sundial we have would be accurate even for Melbourne. Such is life ... we are happy with the sundial we have but are now much more aware of various aspects about them.