Harvard University OSETI Under the direction of Professor Paul Horowitz (visit the homepages of OSETI and the radio projects META and BETA), scientists have equipped the Harvard 61" optical telescope with a pair of very fast photodetectors. The system extracts about 25% of the light collected by the telescope while it is being used to study the radial velocities of 5000 nearby stars. The experiment is thus a "piggyback" system and uses light that cannot be used by the main experiment's echelle spectrograph. The system uses two detectors in a "coincidence" system - both detectors have to register a pulse at the same time for it to be recorded. This is because these detectors are prone to random "false" detections and by using two, the number of false alarms is greatly reduced. A "real" signal of more than 100 photons will always trigger both detectors and then the time, the sky coordinates of the signal and the details about the pulse will be recorded ("logged") by a PC. Tests of the system are regularly made by means of a strong lightsource (a fast light-emitting diode [LED]). No clear detections yet "First light" on this system was on 19th October 1998, and by early 2001 the system had made over 17,000 observations of 5000 target stars. In the first 27 months of observations, 191 "events" were observed from 160 stars (out of 3400 observed at that time). This corresponds to a rate of 0.7 per night. There is no clear evidence that those "events" are the true detection of short pulses of light from the stars and tests are continuing to track down their origin. They could, for example, be from local events such as cosmic-ray particles (muons), or atmospheric Cerenkov flashes that are produced when extremly energetic cosmic particles pass through the atmosphere. One way out of this problem is to use two, well separated, telescopes. An identical set of equipment is now being mounted on a recently restored 36" telescope operated by astronomers at Princeton University. Next step: the Harvard All-Sky Optical SETI survey Funded by the Planetary Society, Paul Horowitz and his collaborators are now building a short-focus 1.8-metre optical telescope. The telescope can point only along the meridian line (north-south) but it moves up and down so that it can observe stars at any altitude for each night's observing run. As the earth rotates, a strip of sky will pass across the field-of-view of the telescope, measuring 1.6° by 0.2°. The stars that cross that field of view will be observed by a grid of 1024 nanosecond-speed pulse detectors. Over a period of about 200 clear nights, this telescope will be able to survey a substantial part of the sky (between -20° to +60° declination) with each spot on the sky being observed for 48 seconds. It will be exciting to learn whether it detects those possible bright bursts of laser light from other civilisations!

The Harvard "piggyback" pulse detection system mounted on the 61" Telescope. Plans for the Harvard 1.8-m optical all sky survey telescope.