The acronym SETI stands for the Search for ExtraTerrestrial Intelligences. The SETI League, Incorporated is a non-governmental, non-profit organization with members ranging from professional astronomers to grassroots amateur enthusiasts, corporate research divisions to University astronomy departments. The fundamental desire of all members is to advance the technological capabilities made available to SETI searches and ultimately secure evidence of a technologically advanced extraterrestrial civilization.
Many people may wonder why success has not already been announced or failure been recognized and accepted. It can be hard for us to truly understand the sheer scale of even our Milky Way galaxy, let alone the Universe. And even those that do might question the point of detecting a civilization some vast interstellar distance away, beyond 500 light years of our solar system. What many fail to realize is that detecting even a close extraterrestrial civilization on a technological par with ourselves is likely to be extremely difficult!
Numerous science fiction stories have alien invaders arriving above Earth having detected our electromagnetic communications signals in the vastness of space, but how realistic is that really? The science fiction novel "Contact" by Carl Sagan involved a return message of underlying layers of complexity with the top layer Hitler's limited television broadcast at the 1936 Olympic Games. In 2009, that transmission has traveled 73 light years, but the likelihood that it was decipherable even past the boundary of our solar system is extremely remote.
The Arecibo broadcast, the one radio transmission we have deliberately sent intended for extraterrestrial beings, was a very strong directional transmission intended to traverse intergalactic space to the globular star cluster M14; we sent it in 1974 but it will take 21,000 years to reach M14. Most of our communications these days are targeted up to satellites, then beamed down from them. Broadcast signals by their very nature dissipate rapidly over distance. Is it likely that such signals might cross interstellar distances? Are they likely to even get to the edge of our solar system without distorting so much that they are indistinguishable from background noise? We don't actually know.
The same will apply to a nearby extraterrestrial civilization technologically equivalent to ourselves. The chances of detecting them if they do not send a transmission our way is small. And these are our potential near neighbors! Project Phoenix by the SETI Institute has been examining nearby stars since 1993, but with no success to date. But there is no reason to consider that surprising. Even if an ET civilization on a nearby star did send us a message, we would need to be looking in the right direction at the right time. Our one message from Arecibo was only 3 minutes long!
What the SETI League, Incorporated provides is a place for the various SETI efforts to achieve a forum, a place of mutual discussion and support. It also links members into Project Argus, named after a creature with 100 eyes from Greek mythology.
The objective of Project Argus is to link 5,000 or more small radio telescopes belonging to SETI League, Inc. members in an all-sky perusal of microwave signals. Providing a continuous monitoring of the heavens, from every direction, for the first time ever in human history. It started on the 21st of April, 1996 with just 5 radio telescopes; rather appropriately, that day was Earth Day. In November of 2000, Argus reached its namesake, with 100 radio telescopes linked together. Unfortunately, radio telescopes are not cheap. The enthused goal of reaching 5000 radio telescopes by 2001 without government funding fell far short. As of a 2008 report, there are just 142 radio telescopes devoted to Project Argus. Conspiracy theorists might quite legitimately wonder at why this noble investigation is so dramatically failing to even vaguely approach its desired monitoring network.
Nevertheless, the SETI League, Inc, continues in its efforts and remains the fundamental link between the professional investigators of our skies and the ardent amateurs.