Communications

All through history people have used the light of the Sun to communicate with each other. Even today you can "harness the Sun" to communicate. The ancient Greeks used sunlight to communicate with each other. The Greek historian Herodotus tells us that the Greeks used a polished mirror to reflect sunlight and send signals. This is what is known as heliograph signaling.

Ships used light flashes to communicate with each other long before the radio was invented. Armies employed the same technique to communicate on the battlefield. However light signals do have their problems. Despite the fast speed at which light travels, a message can only travel as far as one can see. Light signals work best on a level plain and at sea and obviously will not work well in mountainous regions unless the people trying to communicate do it from the tops of peaks. Even in situations at sea or in level areas the light will eventually be cut off by the curve of the earth.

You can try communicating using the Sun. All you need is a friend, two mirrors, and a sunny day. Go outside and stand facing your friend and so that the light will strike your mirror. Determine what your signals will mean and give it a try.