Scientific Newsletter - March 29, 2000
Ron Hipschman, Dan Werthimer
SETI@home collects its data from the world's largest radio telescope in Arecibo, Puerto Rico. We've been recording data at the Arecibo telescope since December 1998, and analysing that data (with your help!) since May 1999.
SETI@home is a very fortunate science program. It utilizes 70% of the Arecibo telescope time. The other 30% is time used for repair, maintenance, or radar observations (Arecibo's powerful radar transmitters create too much interference for SETI@home's sensitive receiver).
This is an extraordinary amount of telescope time! Most astronomers are lucky to get even a day a year on the telescope for their research. Since SETI@home doesn't need to point to any specific point in the sky, it just "goes along for the ride" while other astronomers use the giant antenna. If SETI@home could take data full time we would collect about 50 GB of data every day. It takes us about eight months to "cover" the Arecibo sky. This isn't 100% of the sky that is visible to the telescope since we don't control pointing, but it's close. Our goal is to collect and analyze at least two years worth of data. This would allow us to cover the sky seen from Arecibo about three times.
Why would we want to cover the sky three times? Redundancy is important to us. Why? First, the radio signals may not be "on" all the time. Our distant friends may not be transmitting continuously, or their transmitter may be located on a rotating planet and thus not visible constantly. Second, the source can "scintillate". This means that the signal level will rise and fall because of the interstellar medium between us and the transmitter. This would cause a distant source of radio signals to rise and fall in intensity with a time scale of about one hour. Third, and most importantly, we need to record the data three times for verification. Any strong signal must first be verified by seeing it more than once. This helps rule out, though not eliminate the possibility, that the signal is radio frequency interference (RFI). Of course extraordinary sources are still interesting, even if we see them only once!
SETI@home now has enough computer power to analyze almost all the data that we've gathered to the present time and, we can keep up with the data as it comes in from Arecibo. Due to the generosity of the SETI@home community, the project hopes to deepen the analysis in the client to add pulse detection. We plan to add this in version 3 of the client. Given enough additional funding, in future versions of SETI@home, we hope to increase the bandwidth searched, and expand the search in other parts of the sky using other radio telescopes around the world. More about this in future newsletters...
What have we done with your data? So far we've concentrated on the strong gaussians. These represent the best possible signal sources. This is like skimming the cream, there's lots more we'll be doing with the data in the future. We've found several extremely strong signals. Unfortunately , none of these have turned out to be extraterrestrials. Upon re-analysis of the signals (either by SETI@home Berkeley, or by re-sending them to a different client), all have turned out to be radio frequency interference, or test signals we inject into the data stream to monitor system, or improperly processed work units (computer error, communication error, or on rare occasions, intentional faking of data).
Don't get discouraged. We're searching for a very small needle in a very large haystack, and we're just barely looking in a small corner of that haystack. Every project must start with baby-steps and learn as it grows. Given the increasing sophistication of home computers and signal processing technology, we'll keep improving our techniques by leaps and bounds.
So keep those clients running! We're extremely grateful for your participation. You've helped build our planet's largest supercomputer!
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