Radar: A Silent Eye in the Sky Today's society relies heavily on a taken-for-granted invention: radar. Almost everyone uses radar, whether they realize it or not. Tens of thousands of lives rely on the accuracy and speed of radar to guide their aircraft through the skies unscathed. Others simply use it when they turn on the morning news to check the weather forecast. Even though radar seems to be an important part of our daily lives, it hasn't been around for very long. It did not go into effect until 1935, close to World War II. Both the British and the Americans worked on radar, but they did not work together to build a single system. Each of them developed their own systems at the same time. In 1935, the first radar systems, called the Early Warning Detection system, were installed in Great Britain. In 1940, Britain and the United States installed radar on board fighter planes, giving them an advantage in air-to-air combat and air-to-ground attacks. Radar works according to a relatively simple theory. It's one that everyone has experienced in their life. Radar works much like an echo. In an echo, sound is sent in all directions. When sound waves find an object, such as a rock face, they bounce back towards the source of the echo. If you count the number of seconds that passed from when the sound was made to when it was heard, you can calculate the distance the sound had to travel. The formula is: (S/2) someone shouting and listening to the echo. In fact, modern radar listens not only to the echo, but also where the echo comes from, in which direction the object is moving, its speed and its distance. There are two types of modern radar: continuous wave radar and pulse radar. Pulse radar works like an echo. The transmitter emits short bursts of radio waves. It then turns off and the receiver listens for echoes. Pulse radar echoes can indicate the distance and direction of the object creating the echo. This is the most common form of radar and is the one most used today in airports around the world. Continuous wave radar works on a different theory, the Doppler theory. Doppler theory works on the principle that when a radio wave of a set