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 May 23,
1999: The Arecibo Observatory, the world's largest
radio telescope, completely fills a natural karst valley
in the Carribean island of Puerto Rico.
The 1000 ft diameter reflector is so big that
scientists actually run around it for exercise. Many discoveries
are credited to the great dish, including the first known extrasolar
planets orbiting a neutron star,
relativistic binary pulsars that spectacularly confirm Einstein's theories,
and thousands of new galaxies that delineate the structure of
the local Universe.
Right: The 1000 ft. (305 m) diameter Arecibo radio telescope is the largest single-dish telescope in the world. The spherical dish is too large to move. Pointing is accomplished by the rotation of the earth. A 40-degree wide band of the sky parallel to the celestial equator is visible to the telescope. More information.
SETI@home - a free screen-saver program that sifts through data from the Arecibo Observatory in search of extraterrestrial transmissions-- was made available on-line for the general public on May 17, 1999. The program is easy to download and install. Downloading requires about 5 minutes over a 28.8Kbps modem. "Installing it was no problem," said Science@NASA artist Duane Hilton, a self-professed technophobe. "If I can do it anyone can!"  from UC Berkeley!
The program literally runs itself. Whenever your computer is idle, the SETI@home screen saver pops up and begins to analyze Arecibo data fetched from a web server in Berkeley, CA. SETI@home connects to the Internet only when it needs to transfer data. This occurs once every few days and lasts for about 5 minutes. 
Left: A picture of the SETI@home screen saver in action.
In only one week since SETI@home's official release, 298,000 computers have devoted over 9.5 million hours of CPU time to the project. That's 1100 years of CPU time, and the totals are mounting! [See: SETI@home usage statistics] SETI@home organizers are understandably excited. Louis Friedman, Executive Director of the Planetary Society, which sponsors SETI@home, said, "With SETI@home, anyone, anywhere could be the person who helps discover intelligent life elsewhere in the universe. This is a grand experiment - in science, in technology and in society - and a global cooperative effort at the frontiers of knowledge." Data for the SETI@home project are collected by an instrument at Arecibo called SERENDIP IV, which was installed in September 1998. A dedicated receiver tuned to a frequency near 1420 MHz collects signals from the sky 24 hours a day, seven days a week (except during periods of maintenance and testing). The data are recorded on tape and also fed to the 160 million channel SERENDIP spectrum analyser. Every 1.7 seconds SERENDIP checks the latest data and looks for very narrow bandwidth signals of the sort expected from extraterrestrial radio transmitters. Candidates are logged and stored for follow-up analysis and/or confirmation. 
The observing frequency, 1420 MHz, corresponds to the wavelength
of radiation produced by a quantum mechanical "spin-flip transition"
in neutral hydrogen atoms.
Because hydrogen is the most abundant element in the Universe
and because
1420 MHz is a relatively quiet frequency free from sources of
natural radio interference, many SETI experts think that 1420 MHz
is a
good place to tune in interstellar broadcasts. Would aliens
reason the same way?
There's no way to know, but the search has to start somewhere.
The SERENDIP program runs "piggy back" on other, more conventional observing programs. For example, while one astronomer might use Arecibo's Gregorian feed system (pictured below) to track and study pulsars, SERENDIP collects data from the 1420 MHz feed located near the 400 MHz feed at the other end of the rotating platform suspended above the reflecting dish. As the Gregorian reflector tracks the neutron star, the 1420 MHz feed points at some random area of the sky typically 10 to 20 degrees away. Rather than focus on particular nearby stars, SERENDIP will survey all of the sky visible to the Arecibo telescope. Planners reasoned that we know so little about extraterrestrial intelligence that signals might come from any direction. Over the next two years the Arecibo piggybacking observations are expected to cover about 30% of the entire sky three times. 
Left:
Suspended 450 feet above the spherical Arecibo dish is a
900 ton platform that supports a variety of receivers and antenna feeds.
The triangular part of the platform is fixed. It
supports a rotating bow-shaped
structure with a Gregorian secondary reflector on
one side and
a carriage house
for tunable "line feeds" on the other. The dome and
the carriage house
ride on tracks -- they can be pointed up to 20
degrees from the vertical.
The 1420 MHz SERENDIP receiver uses a line feed attached to the
carriage house on the right. In the picture a
400 MHz line feed is visible, but the smaller
1420 MHz feed is not.
Most of the SETI programs in existance today, like SERENDIP, use powerful computers that analyze data from the telescope in real time. Because flow of data is so rapid and voluminous, there's no time to look very deeply at the data for weak signals nor do they look for a large class of signal types including "chirped" and pulsed transmissions. To tease out the weakest signals, a great amount of computer power is necessary. This is where SETI@home comes in. By combining the power of hundreds of thousands of PCs on the internet, SETI researchers hope to discover elusive signals that SERENDIP's quick look approach might have missed. Click to learn more about SETI@home signal analysis. 
If such a signal is found using the SETI@home program, the person whose computer crunched
that vital bit of data will go down in history as helping to forever alter humanity's view of our place
in the universe.
Right: The SERENDIP III instrument in action at Arecibo Observatory. The diagonal line on the screen is a drifting test signal being run to check the system. Serendip III is the predecessor of SERENDIP IV. Initial funding for the SETI@home project came from the Planetary Society. Other sponsors include the University of California Berkeley, Sun Microsystems, Fujifilm Computer Products, and Informix. Paramount Pictures provided funding to the Planetary Society for this project in connection with the opening of the movie, "Star Trek: Insurrection." The acronym SERENDIP stands for Search for Extraterrestrial Radio Emissions from Nearby Developed Intelligent Populations. |
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SETI@home home page -- at Berkeley SETI@home FAQ -- from the SETI@home web site The Planetary Society -- home page Arecibo Observatory -- home page Arecibo Observatory -- descriptive information The SERENDIP Project -- learn more about the piggyback SETI effort at Arecibo SERENDIP -- slide show The SERENDIP Newsletter -- Fall 1997 Arecibo: the largest telescope -- Astronomy Picture of the Day, Nov 29, 1998 How to search for aliens -- Astronomy Picture of the Day, May 17, 1999 An anomalous SETI signal -- Astronomy Picture of the Day, Mar. 30, 1999 Radio, the Big Ear, and The Wow! Signal -- Astronomy Picture of the Day, Sep. 17, 1998 |
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