Sundials and sand clocks

Posted in 7 - How things work, Pendulums and clocks

Long time ago, before there were clocks with hands, the men used the sun to tell the time.


When the sun shines, a stick stuck in the ground casts a shadow that moves around the stick on the opposite side to the sun. In the morning, the shadow is long.

At noon, the shadow is short.

In the afternoon, the shadow is long again. When it was discovered that the shadow always moves at the same speed, the sundial began to be used to measure time.


To measure time, formerly they also used hourglasses. The hourglass is made up of two blisters joined by a very thin neck. The sand takes an hour to pass

of the upper blister,

through the neck,

to the lower blister.

There are smaller hourglasses.

The sand takes only three minutes to go from a blister to another.

They are very useful for timing long distance conferences or cooking eggs.

The sundial is a rod that casts the shadow on a clock face on which the hour numbers are marked..

At noon, the sun is at the highest point of the path you travel during the day. The shadow of the rod is projected on the 12.

The shadow of the rod runs through the numbers as the position of the sun in the sky changes.

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