Radio Astronomy

The presence of radio sources in outer space was an important breakthrough for astronomers. Prior to the 1930s, astronomers had to rely almost entirely on visible light for the information they obtained about the solar system and outer space. Sometimes that light was collected directly by the human eye, and others time by means of telescopes. But in either case, astronomers had at their disposal only a small fraction of all the electro-magnetic radiation produced by stars, planets, and interstellar matter.

If an observer is restricted only to the visible region of the electromagnetic spectrum, she or he obtains only a small fraction of the information that is actually emitted by an astronomical object. Jansky's discovery meant that astronomers were now able to make use of another large portion of the electromagnetic spectrum—radio waves—to use in studying astronomical objects.

In some respects, radio waves are an even better tool for astronomical observation than are light waves. Light waves are blocked out by clouds, dust, and other materials in Earth's atmosphere. Light waves from distant objects are also invisible during daylight because light from the Sun is so intense that the less intense light waves from more distant objects cannot be seen. Such is not the case with radio waves, however, which can be detected as easily during the day as they can at night.