Sundials

Put a stick upright in the ground. Congratulations, you have made a very crude sundial. The shadow cast by the stick will move throughout the course of the day just as the hour hand of a clock moves. Every hour make a mark where the shadow is and you have a sun clock. This will give you a rough idea of what time of day it is but not a very accurate one. Why not?

The problem is that at different times in the year the Sun is higher or lower in the sky. The angle that the shadow moves in a certain time is different because of this.

What the sundial reads depends on your latitude

So, if you set up a sundial in the middle of summer it will not be accurate a few months later. The solution is to mount the stick at an angle. It should lean to the north at an angle equal to the latitude of the location where the sundial is. The gnomon should be parallel to the Earth's axis.

The sundial above is called an equatorial sundial. There are several other types.

The lines on the base of a horizontal sundial, e.g. the one above, are worked out using a complicated mathematical formula. There are plenty of places on the internet where you can download a template.

Have a look at www.sundials.co.uk for lots of different designs.

    
Images with kind permission from www.sundials.co.uk

Bear in mind that your sundial is telling you your local solar time. Unless you live on the same longitude as Greenwich this will be slightly different to what your watch says.