Optical telescopes are limited to those wavelengths that the human eye can detect. However, information also comes to us at other wavelengths. In addition to the visible radiation that normally penetrates the Earth's atmosphere on a clear day, radio radiation also reaches the ground. Radio astronomers have built many ground-based radio telescopes capable of detecting cosmic radio waves. These devices have all been constructed since the 1950s. Radio astronomy is a much younger subject than optical astronomy.
Radio messages would be a much more practical way to find out if intelligent life forms exist in space. Dr. Sabatino Sofia, professor of Astronomy, gave the following analogy in comparing space travel and radio astronomy: "If you wanted to find out information about someone in Europe, would you take an airplane and travel there or would you pick up the telephone and call the person?"
In 1960, radio Astronomers observatory on Green Bank, West Virginia studied the radio emissions coming from two relatively nearby stars. Both of these stars were about 10 light years from Earth and both were thought to be the type of star that is long-lived and stable enough to allow life to develop. There was no evidence of planets around either stars, but that doesn't mean that there are none. At such distances from us, planets are too small and dim to detect.
Radio and other nonoptical telescopes are essential to study of the Universe because they allow astronomers to probe regions of space that are completely opaque to visible light and to study the many objects that emit little or no optical radiation at all.