Radio
The SETI project has for the past several decades been conducting a search for signals being transmitted by extraterrestrial life located outside the solar system, primarily in the radio frequencies of the electromagnetic spectrum. Special attention has been given to the Water Hole, the frequency of one of neutral hydrogen's absorption lines, due to the low background noise at this frequency and its symbolic association with the basis for what is likely to be the most common system of biochemistry (see Alternative biochemistry).
The regular radio pulses emitted by pulsars were briefly thought to be potential intelligent signals; the first pulsar to be discovered was originally designated "LGM-1", for "Little Green Men." They were quickly determined to be of natural origin, however.
Several attempts have been made to transmit signals to other stars as well, see "Realized projects" at Active SETI and Interstellar Radio Messages. One of the earliest and most famous was the 1974 radio message sent from the largest radio telescope in the world, Arecibo, in Puerto Rico. An extremely simple message was aimed at a globular cluster of stars known as M13 in the Milky Way Galaxy and at a distance of 30,000 light years from our solar system. These efforts have been more symbolic than anything else, however. Further, a possible answer needs double the travel time, i.e. tens of years (near stars) or 60,000 years (M13). Sending Interstellar Radio Messages between stars may prove to be optimal for many applications.
Read more about this topic: Interstellar Communication
Famous quotes containing the word radio:
“Local television shows do not, in general, supply make-up artists. The exception to this is Los Angeles, an unusually generous city in this regard, since they also provide this service for radio appearances.”
—Fran Lebowitz (b. 1950)
“All radio is dead. Which means that these tape recordings I’m making are for the sake of future history. If any.”
—Barré Lyndon (1896–1972)
“from above, thin squeaks of radio static,
The captured fume of space foams in our ears—”
—Hart Crane (1899–1932)