Making a horizontal sundial

To make a horizontal sundial you need a gnomon (a pointer with an angle equal to your latitude) and a horizontal scale. You will also need a compass to set your gnomon and scale so that it lines up with the north- south line where you are.

The horizontal, scale should look like the one drawn below. The lines show the hours. This one is correct for a person at 51^o N, you will have to use the table below to draw your own if you live at another latitude.





The table below shows the angle A for different hours at various latitudes

Hours from noon	50	51	52	53	55
1	11.6	11.8	11.9	12.1	12.4
2	23.8	24.2	24.5	24.7	25.3
3	37.4	37.8	38.2	38.6	39.3
4	53.0	53.4	53.8	54.1	54.8
5	70.7	71.0	71.2	71.4	71.9
6	90.0	90.0	90.0	90.0	90.0

The angle from the noon line (12:00) is called the hour angle (H). Since the Sun moves through 15^o each hour the hour angle is 15 x the number of hours from noon.

You can calculate the angle (A) from the noon line for various hours using your latitude (L).

A = tan^-1[sin L x tan H]

Don't forget to change the angle of your gnomon to that of your latitude.