 |
||||||||||
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
|
 |
|
|
|
|
|
|
|
|
|
|
SETI
- Allen Telescope Array
- Optical SETI
- Interstellar Message Construction
- Project Phoenix 1995-2004
- Background Science
- History of SETI
- Center for SETI Research Team
- Other people doing SETI
- Hollywood's View of SETI
Life Without Lovell
by Dr. Peter Backus, Observing Programs Manager
Something is missing. At least this is how it feels each evening around five in the evening. As those who follow our observing sessions know, we are no longer using two sites; thus we have bid farewell to Jodrell Bank Observatory, our secondary site during previous runs.
Although I spent observing sessions in Arecibo, I visited Jodrell Bank, or JBO twice; once to help set up racks for the new search system, and once to pack up those same racks. Although I only spent a few weeks there, I have fond memories of the friendly observatory staff, the beautiful Cheshire countryside, and the traditional English breakfast.
Up until this session, my only regular contact with JBO while I was in Arecibo was to punch in a fifteen-digit phone number at 5:00 PM, and ask the telescope operator to prepare the Lovell Telescope for SETI observing. Of course Id also talk to our staff on duty there, to make sure we were all ready to observe. It was always quite a treat chatting with Ian Morison, the personable JBO staff astronomer assigned to help us out. How I do miss the Lovell Telescope -- and not just because of the English bacon and conversing with Ian.
We used the venerable 250-foot telescope to check candidate signals. Using the characteristics of a signal measured at Arecibo, we predicted what that signal should look like Jodrell Bank. The two observatories have greatly different positions in latitude and longitude, causing the signal to shift frequency and frequency drift rate by predictable amounts. It was a great way to discriminate against terrestrial signals. Unfortunately, the Lovell Telescope lacked a receiver at S-Band, a feature that we require to cover all the frequencies of the Project Phoenix target stars.
With a single telescope we must use more time-consuming methods to sort out radio interference. In some frequency bands, terrestrial signals are so strong and widespread that we simply exclude those frequencies. For the rest of S-Band, a database of interference signals is our first line of defense. After each SETI observation, we compare any detected signals with the database. Any new signals are tested with another observation on the position of the star. We call this observation an ON. (Yes, the original observation was also ON but the computers treat the data differently for this observation since we are checking a potential ET signal.)
Most terrestrial signals disappear in the ON. Many of these are from satellites that have moved below the horizon in the few minutes between observations. Others are ground based transmitters, which are no longer detected by the antenna once it has rotated enough while tracking the star. In other cases, the transmitter simply turns off. We expect that an ET transmitter, especially an intentional beacon, will keep transmitting and be detected in the ON.
Unfortunately for us, some terrestrial signals also persist in the ON. In this case, we move the telescope to an OFF position, away from the star. If we continue to see the signal when not pointing at the star, its not coming from the star and is added to the interference database. If the signal disappears in the OFF position, we repeat the observation on the stars position. If the signal reappears, we start to become interested.
The whole process is less efficient and requires much more attention from the observer, which is actually fun for a while. Still, at times I find myself wishing I could punch in that long phone number and hear a British accent say Good evening, Jodrell Bank.