Unlike optical telescopes, radio telescopes can be made of durable materials that are exposed directly to the elements of nature without being damaged or affecting the quality of the signal. This is fortunate because radio signals received from space are very weak, requiring large dishes and long observing times to collect useful data. Additionally, multiple dishes can be linked by computer to form a single radio telescope called an array. The Very Large Array ( VLA ) and Very Long Baseline Array of the National Radio Astronomy Observatory ( NRAO ) are examples of such arrays. Each antenna in the VLA measures 25 meters in diameter and weighs about 230 tons.
Radio telescopes are mainly used for radio astronomy, but are related to ufology because of their association with SETI projects. On August 15 1977, a radio telescope nicknamed The Big Ear at Ohio State University recorded a 72 second transmission emanating from the direction of the Chi Sagittari star group. It was dubbed the Wow signal because it fit the pattern that SETI scientists were looking for. Unfortunately repeated searches using other radio telescopes including the VLA have not been successful in re-acquiring the signal. If the signal was from an extraterrestrial transmitter, there are not many explanations as to why it has not reappeared. The most likely is that if the ET technology and operational procedures are similar to those on Earth, they will be doing a lot more listening than transmitting. Compared to the time spent listening, Earth has contributed only a tiny fraction to the cosmic bulletin board. The earliest that any message sent from Earth is anticipated to reach its destination is in the year 2029. Titled "A Message From Earth", it was transmitted from the RT-70 radar/radio telescope operated by the State Space Agency of the Ukraine to the planet called Gliese 581c located approximately 20 light years from Earth.