Midday line determination by means of gnomon.

At midday the shadows of all the objects are directed along the line pointing exactly from the South to the North. This line is called midday line. The direction of the line helps to set the sun-clock.

We cen determine the direction of midday line in any point on the Earth with the help of an ancient astronomic device - gnomon. To make it you should use a straight pole, to strike it into the ground vertically, using a plumb. At one or two hours before midday mark the shadow edge from the pole with the help of a peg.

Take a cord. One of its ends tie to the base of gnomon. Using the free part of the cord as a circle draw a circumference coming through the peg.

The shadow from the pole will decrease first then increase and slowly turn. When it again touches the drawn circumference mark the shadow edge with another peg. A straight line coming through the middle of the line, connecting the first and the second peg and the base of gnomon is a midday line. Now we can determine the time of the true midday in any moment. Observe if it coincides with the midday time on your watch.

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