Analemmatic Sundial - Epping Forest, Essex, UK - Outdoor Interactive Science Displays on Waymarking.com

The "path" with the months marked on it is orientated in a north south direction with the "hour" marker stones set around it. Close west is an information table that tells us:

This is an analemmatic sundial and the hour posts are set out according to unique calculations prepared for this locality.

Instructions for telling the time by the analemmatic sundial

1. Stand on the paving stones along the north/south centre line according to today's date with your back to the sun and raise one arm above your head.

2. Now look at your shadow which will be pointing towards the hour posts. This will show the local sun time.

3. The sun's rays fall here at High Beach 10 seconds before they reach Greenwich. As the difference is so small, it is really the same as Greenwich Time. (Other places further east or west will be aout by a greater amount).

4. Because the earth goes round the sun in an elliptical path, the sun appears to vary its speed throughout the year and it can be up to a quarter of an hour fast or slow compared with an accurate clock. To work out the true time, you must apply the correction called the Equation of Time, as shown in this graph, to obtain Greenwich Mean Time.

5. Of course we have to add an hour to give British Summer Time.

This sundial was designed and donated to the Epping Forest Centre by Comdr. Richard Andrewes.

The Maths website tells us about an analemmatic sundial:

We often take the problem of telling the time or of finding the day's date for granted, but finding solutions to both of these questions is vital to our civilisation. Early men and women needed to have an accurate notion of the seasons in order to know when to plant and harvest their crops. As civilisation developed it became important to know the time during the day. Two times were obvious as everyone was aware of when the sun rose (dawn) and when it set (dusk). More accurate observations of the sun then showed that having risen in the East, it climbed to its highest point in the sky (due South in the Northern hemisphere) before descending towards its setting point in the West. The time of the highest point reached by the sun (which is when the shadows were shortest) is called Noon. Knowing dawn, Noon and dusk gave us morning, afternoon and night.

Every civilisation has been interested in the way the sun moves, and astronomy and mathematics have always developed alongside each other. Better observations called for quicker and more efficient mathematical methods. More detailed theory drove people to make more accurate observations. In this way both theory and practice evolved together. In this article we give some theory about the way the sun moves and then concentrate on a practical method for building a type of sundial known as an analemmatic sundial. We choose initially not to give too much justification for the mathematics behind the construction of this dial. Details of the theory of this dial can be found in a later section of this article.

Note that the following article assumes that you are in the Northern Hemisphere. If you want to build a sundial that is to work South of the equator you will need to make some changes, but the following method is easy to adapt.

What is an analemmatic sundial?
An analemmatic sundial is a particular kind of horizontal sundial in which the shadow-casting object is vertical, and is moved depending on the date, or to be more precise, depending on the declination of the sun on a given day. The time is read from the dial by noting where the shadow cast by the vertical pin crosses hour points laid out on an ellipse. If we make the dial on the ground and large enough, we can use the shadow cast by a person. This makes it very different from the traditional sundial we see often in parks and gardens where the shadow is cast by a triangular shaped wedge. The analemmatic sundial is perfect as a piece of large mathematical sculpture.

Scientific Principle(s) being demonstrated: How a sundial works Briefly explain if the experiment was effective for you. Could it have been better?: Yes, when applying the correction and the hour for BST it was spot on - if I used my left arm! When is the apparatus/experiment available to the public: Dawn to dusk. It's a bit pointless going when the sun is down!

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