Ask Dr. SETI ®

The Doctor Responds:
My calculations indicate that incidental radiation from Earth-like technology could be detected out to at least 1000 LY by our larger SETI telescopes (such as the ones used in the SETI Institute's Project Phoenix targeted search). Since our members' own privately owned and operated radio telescopes are much smaller and less sensitive, it is unlikely that we would be able to detect such incidental radiation from any but the very nearest stars. For example, a one Megawatt transmitter driving a 100 meter diameter antenna can be detected by the typical amateur SETI station at a distance of 1 parsec, which is slightly less than the distance to the nearest star. Our private search hopes to encounter either significanlty more powerful transmissions, or highly directional beacons. Thus the two approaches (sky survey and targeted search) are complementary; see this article for elaboration.

The actual range over which we can hear a signal depends upon the transmit power and antenna gain of the civilization we are trying to detect -- factors over which we have no control whatever. It is interesting, however, to speculate, and to test the results of our best guesses as to extra-terrestrial technology. The spreadsheet programs "linkanal.xls" and "ranganal.xls" allow you to evaluate your own what if scenarios. They may be downloaded from here. Using such mathematical tools as these, your guess will be as good as mine!