Microwave and optical (both infrared and visible) radiation are the basis for the principal plans in use or under discussion for searching for advanced extraterrestrial societies, but we should be on the alert for alternative modalities that might contribute. Among the latter are other forms of radiation, matter transfer, and a variety of exotic suggestions.

The SERENDIP SETI group is currently conducting search operations on the world's largest radio telescope at the Arecibo Observatory in Puerto Rico. The third generation SERENDIP system, SERENDIP III, is a 4 million channel Fast Fourier Transform-based spectrum analyzer with 0.6 Hz frequency resolution. In this talk we will discuss results of our recent 3.5 year sky survey. SERENDIP has looked at 95 percent of the sky visible from Arecibo in the range from 424 to 436 MHz, analyzed 1.5 X 10¹⁴ spectral bins, and logged information on over 300 million signals. The fourth generation SERENDIP system expands on the SERENDIP III design. SERENDIP IV computes 200 billion operations each second providing spectral analysis on 168 million channels every 1.7 seconds. We will also discuss the design and use of the SERENDIP IV system and future observing plans.

Project META (Megachannel ExtraTerrestrial Assay), a full-sky survey for artificial narrow-band signals, has been conducted from the Harvard/Smithsonian 26 m radiotelescope at Agassiz Station and from one of the two 30 m radiotelescopes of the Instituto Argentino de Radioastronomia (IAR). The search was performed near the 1420 MHz line of neutral hydrogen, and its second harmonic, using two 8.4 X 10⁶ channel Fourier spectrometers of 0.05 Hz resolution and 400 kHz of instantaneous bandwidth. The observing frequency was corrected both for motions with respect to three astronomical inertial frames, and for the effect of Earth's rotation, which provides a characteristic changing signature for narrow-band signals of extraterrestrial origin. Among the 6 X 10¹³ spectral channels searched in the northern hemisphere, Horowitz and Sagan reported 37 candidates events exceeding the average threshold of 1.7 X 10^-23 W m^-2, while in the southern hemisphere among 2 X 10¹³ spectral channels analyzed we found 19 events exceeding the same threshold. The strongest signals that survive culling for terrestrial interference lie in or near the Galactic Plane. The first high resolution southern target search around 71 stars (-90 degrees <EQ (delta) <EQ -10 degrees), was performed, using the facilities of IAR. For this search, we have selected, 'all' the stars at distances nearer than 5 pc and those stars that are falling between +0.6 and +1.0 in the (B-V) color index, with spectral class V, that are at distances nearer that 15.5 pc. Stars bluer that +0.6 have main sequence lifetimes that are too short to provide long-term environmental stability, while stars redder than +1.0 cannot presently be detected. The observations were done with the same spectrometer, tracking each star, at least for 60 minutes, at three different epochs. The third part of the program consisted in observing simultaneously identical celestial coordinates (-30 degrees <EQ (delta) <EQ -10 degrees) between the Harvard/Smithsonian and the IAR's radio telescopes. Finally, we use the Cordes-Lazio-Sagan Model based in scattering theory, simulations and empirical constraints on interstellar scintillations to discuss the intermittency of radio signals from extraterrestrial intelligence. It is showed that these narrow-band non-repeating 'events' found by Project META can be generated by (a) radiometer noise fluctuations, (b) a population of constant galactic sources which undergo deep fading and amplification due to interstellar scintillation, consistent with ETI transmissions and (c) real, transient signals of either terrestrial or extraterrestrial origin. The Bayesian test shows that hypothesis (b) and (c) are both highly preferred to (a), but the first two are about equally likely. Using this analysis we discuss the best observing strategies to determine the real origin of these 'events'.

From February 2 until June 6 of 1995, the Phoenix Team conducted SETI observations using the 64 m radio telescope at Parkes and a remotely operated 22 m antenna at Connabarabran. The dual polarization observations covered the frequency range from 1.2 to 3 GHz using a single wideband receiver and two feeds built by CSIRO to support this project. The two antennas simultaneously observed a target list of 202 solar-type stars located at declinations south of -35 degrees. Individual observations lasted up to 276 seconds and examined 20 MHz of the spectrum with resolutions as fine as 1 Hz using hardware pattern detectors to search for narrowband, continuous or pulsed signals whose frequency might be slowly changing in time. The data were analyzed, and candidate signals were identified in near-real-time (before the end of the next data acquisition cycle). Those candidate signals not matched against an on-line RFI database were automatically reobserved with finer resolution by another set of detectors and followed in phase in order to permit a pseudo-interferometric measurement between the two telescopes. This two stage approach (detection on the 64 m antenna and immediate interferometric follow up of candidates) was part of a pipelined observational sequence and proved to be an extremely effective and efficient method of discriminating against RFI. Detection thresholds were set to produce a few candidate signals per observation, yet for more than 23,000 completed observations, the programmed sequence had to be interrupted fewer than 100 times to move the antennas off source for further verification procedures. In each case the candidate signals were found to be of our own technological making. The Phoenix observations in Australia failed to detect any ETI signals, but they also left no mysterious or unexplained signals hanging around. The deployment was a logistical and technological success, and reaffirms our opinion that one telescope is not enough.

In the Search for Extraterrestrial Intelligence (SETI), knowing where to look is important. With hundreds of millions of potential targets, a short list of candidates for targeted searches is a necessity. In the past, target lists were usually based on a simple set of criteria which a potential target star either met or did not meet. Presented here is a quantitative rating system for SETI targets with a sample list of candidates. While this rating system uses assumptions similar to those employed in compiling earlier target lists, here emphasis is placed on using quantifiable properties that could either be directly measured or reasonably simulated to arrive at a numeric rating. The resulting list of SETI targets is not markedly different from those which have been compiled and used to date. Unlike previous lists, however, it can be clearly seen which targets should be given priority over others in a targeted SETI program.

A review of the different proposals made to establish contact with hypothetical planetary neighbors is done. For almost 100 years (approximately 1822-1921) the dominant paradigm for signaling extraterrestrial beings, were based in the exchange of light beam signals. After the success of wireless transatlantic communications and the discovery of radio signals from the cosmos, the main scientific proposals to contact extraterrestrials were based on radio signals. Nevertheless, the development of lasers and other nonlinear optical devices, led into a new set of proposals to use them for interplanetary and interstellar communication means. A review of these proposals and the detection of extraterrestrial technological activities in the optical domain is made. A summary of the requirements needed to explore the astrophysics of shortest timescales is described, in order to develop the nano and sub-nanosecond detectors that could be used to detect interstellar pulsed laser signals.

One of the arguments frequently made against conducting an optical search for extra-terrestrial intelligence deals with the propagation range limitations of optical signals. Examples abound, dating back to the Cyclops report, which show microwave signals to be easily capable of trans-Galactic communications, whereas optical signals reputedly are not. Could proponents of microwave SETI have perhaps overstated the capabilities of their systems, and unwittingly stifled the development of optical techniques in the process? The author, a strong supporter of microwave SETI, concedes the possibility. He reviews the assertion that Arecibo (Earth's largest radiotelescope) would be able to detect its theoretical twin across the Galaxy. This paper challenges the veracity of that widely held belief, through detailed range calculations. It traces the propagation of what the author calls the Arecibo Myth, and explores its impact upon public perceptions as to the validity of SETI acitivites in general, and optical SETI in particular.

Laser technology is a key parameter in optical SETI research. Any detection scheme inevitably depends on assumptions about laser technology available to advanced extraterrestrial civilizations. Without any direct evidence, the best we can do is to extrapolate from present laser technology. To establish a baseline, I will look at past trends, then extrapolate the potentials of important laser technologies.

Can optical SETI contact, and possibly communication, be established via Electro-Optic means, with ETI 'technical civilizations', who like us, potentially might be residing with the galaxy? Specifically, can laser 'Beacons' or interstellar Laser Communications Links (iLCL), be implemented with current or future, but foreseeable Electro-Optic Technology (EOT)? If so, what are the parameters, mechanisms, and concepts by which such systems could be mechanized? If indeed, electro-optic UV/VIS/IR sensors would detect such signals from a remote extraterrestrial origin, from where, and from how far away, might such signals come from? How would we respond to them? The theme, here envisioned, is that a 'Listen-only' strategy could/should be complemented with EOT/laser transmissions by us, terrestrials, so-as to result in a 'receive and transmit' strategy. This form of proactivity could markedly enhance the probability of ultimate successful contact. It is projected, that this can be accomplished by the use of suitably configured, space-based High- Power Laser Sources. Such devices would probably be operating at short optical wavelengths (VIS and UV), into diffraction limited large aperture optics, pointed with high precision and accuracy, at candidate stellar systems. A SNR link-analysis was carried out, for such iLCL systems, in both a pulsed and CW- mode of operation. Laser systems were analyzed whereby a one Mega Watt average output power assumption, was utilized as a baseline. Operating ranges, pulse energies, and pulsewidths were parametrized over a spectrum of optical wavelengths. It is shown that UV/VIS/IR pulsed laser systems operating in the 'Beacon' or lower data-rate mode, might variously operate over such interstellar ranges, 10-3,000 light years at imputed 'optimistic'- and 'nominal'-regimes of likelihood of contact. It is recognized that 'pessimistic'-regime ranges of 3,000-10,000 light years or more, might be required to surmount the Drake Equation probabilities to establish communicative contact. For contact to be made a transmit-receive SYNCHRONISM, accounting for propagation delay time, must exist to enable a 'look' when a signal is present at the reception point. Additionally, a sufficient COEVALITY must exist, to prevent an evolutionary time-phase-delay between communicating agencies, from establishing and maintaining an enduring oSETI-type iLCL contact.

Previous proposals for communicating with extraterrestials have relied heavily on pictorial messages, regardless of whether communicaiton is via electromagnetic radiation or by spacecraft bearing messages. Pictorial messages can be categorized according to whether the pictures can be shown directly or whether they must first be properly formatted. Advantages of more direct representations are suggested, and the universality of pictorial representation is critiqued. An alternative to pictures based on semiotic distinctions is advanced. With this approach, iconic representations, in which the sign bears a physical similarity to that which it represents, are shown directly, rather than in a format that must be reconstructed. This method of communication is illustrated with quantum-mechanical phenomena. The advantages of using this strategy of having the content of a message reflected in the form of the message are detailed.

The vast uncertainties of SETI require caution in discussing the impact of discovery of extraterrestrial intelligence. Despite the awareness of some SETI scientists that such scenarios can easily reflect wishful thinking, popular discussions of the topic are flawed by failure to present speculations regarding impact that are consistent with basic assumptions that make SETI plausible in the first place. A more self-conscious attempt to deal directly with the ethical issues raised by the impact question would aid in creating more rigorous efforts.

'Astronomers find ET civilization.' In the opinion of many, this newspaper headline could reflect what would be the most exciting, challenging and profound discovery not only of the century but of human history. The idea of a plurality of inhabited worlds in the universe is as old as our civilization. It was a religious heresy in pre-Renaissance times; Giordano Bruno was burned at the stake in 1600 because of this belief. A slow but steady increase in the number of papers on the possible existence of other beings distinct from us has been appearing since then. The rapid progress in science and technology, our although poor understanding of the mechanisms of the cosmic evolution, the consolidation of the Darwinian hypothesis and, most importantly, the tenacious work of SETI pioneers have made possibly that the scientific community took seriously the possibility of life in other places of the universe and to search for it. There are different SETI projects running in the world. The unequivocal detection of an ETI signal is the goal. This could take many forms, all of them unpredictable. Some authors notice that the unambiguous confirmation that the signal is of extraterrestrial intelligence origin would be a hard work (Boyce 1990, Tarter 1991). But of most significance is the impact on our society of such a contact. How should we react? With fear and panic because advanced ETIs would quickly destroy the human spirit? Waiting a golden age? Imagine an extraterrestrial spaceship landing somewhere in our planet. What should we do? In both cases, will human behavior be influenced by the incontestable knowledge of the existence of ETIs? As John Billingham point out 'there has been little activity on those cultural aspects of SETI other than science and engineering.'

The problem of alien artifacts on the Earth's Moon has been re-examined. There are many reasons why the Moon is one of the best places to possess evidences of past visitations to the inner solar system by technological alien life, and the reasons are elaborated. The Moon has not been yet examined closely enough to rule out alien artifacts. We must not be too exclusionary of candidates for more in-depth examination if aliens have deliberately camouflaged or simply discarded artifacts without intending for them to noticed. In light of this, search strategies which involve statistical examination of anomalous pixels or searches near unusual resource-bearing places on the Moon (such as the lunar poles, where there may be ice) may prove fruitful, especially if we carefully distinguish between anomalous candidates and actual discoveries of alien artifacts.

The Life in the Universe Curriculum Development project has been a three year program which developed educational materials based on the SETI for use in elementary and middle school classrooms. The process and products are described in this paper.

The Optical Search for Extraterrestrial Intelligence (OSETI) is based on the premise that there are ETIs within our galaxy which are targeting star systems like our own with free-space beams. Upon these beams will ride attention- getting beacon signals and wideband data channels. Perhaps the wideband channels form part of a Galactic Information Superhighway, a Galactic Internet to which we are presently oblivious. The Columbus Optical SETI Observatory described in this paper is intended to be a prototype observatory which might lead to a new renaissance in both optical SETI and optical astronomy. It is hoped that the observatory design will be emulated by both the professional and amateur communities. The modern-day OSETI observatory is one that is more affordable than ever. With the aid of reasonably priced automatic telescopes, low-cost PCs, software and signal processing boards, Optical SETI can become accessible to all nations, professional scientific groups, amateur astronomy societies and even individuals.

A detailed design approach is given for a low-cost, large aperture laser reciever capable of detecting and recognizing short laser pulses of unknown frequency. The design results from development of three basic rules for detection of extraterrestrial signals. The paper looks at both frequency and time domain issues, and configures a specific design to accomplish detection and recognition. This design enables a large aperture system that costs orders of magnitude less than that of a diffraction-limited astronomical telescope of equivalent capability for detection of SETI laser pulses. Implementation of this design will enable the detection of laser signals, if present, that have previously been undetectable.

The current state of the design and development of a modest robotic telescope based on commercially available parts (10 inch Meade Schmidt-Cassegrain telescope, Santa Barbara Instrument Group CCD cameras, OSETI instrumentation, PC computers, Windows 95 operating system) are discussed with emphasis on the application to OSETI. The authors provide an explanation of the software design and its use for remote control purposes via the internet. This software uses the Universal Internet Shell (UIS), and the UIS drives the telescope, CCD cameras, appropriate OSETI instrumentation and communicates with local and remote servers. Also, the UIS receives e-mail messages, prepares lists of observing targets, provides observations and sends accumulated data to the users. The robotic telescopes under discussion was developed to make follow-up observations of gamma-ray-burst optical-counterparts which correlate with data from the Gamma Ray Observatory satellite. However, the system's flexibility allows it to be put to other scientific uses, in particular, for conducting Optical SETI observations. This work is based upon an international cooperative effort between Dr. Stuart Kingsley, Director of The Columbus Optical SETI Observatory and our Ondrejov Observatory in the Czech Republic.

The first three extrasolar planets orbiting Solar-like stars have recently been discovered. All three were inferred from a periodicity in the optical Doppler measurements of their host stars, indicating a reflex motion in response to the gravitational force exerted by the planets. From such measurements and standard Newtonian physics, one may infer the orbital period and value of M_PL sin i of 0.46, 2.5 and 6.5 M_JUP, and orbital periods of 4.2, 117 and 1100 days, respectively. The most massive planet (around 70 Vir) has an eccentricity, e equals 0.38, larger than any in our Solar System, and one (around 51 Peg) has an orbital radius of 0.05 AU which is smaller than any in our Solar System. A general theory for the formation of planets must include these new characteristics.

The idea of interstellar communication with the aid of lasers and the possibility of manipulating natural lasers to this end make the search for lasing cosmic sources a part of the SETI program. Yet, apart from the very weak lasing in the 10 micrometers CO₂ band in the Martian and Venusian atmospheres, only one case of possible natural lasing, in the 4.7 micrometers hydrogen Pf(beta) line from the Becklin-Neugenbauer source in Orion, has been reported but never confirmed. Given hundreds of maser sources detected during the 30 years after their first discover in 1965, the lack of detected natural lasers became a tantalizing puzzle. We undertook a search for high-gain hydrogen lasers in the far-infrared spectrum of MWC349, a peculiar star known as a unique source of mm/submm hydrogen masers. We used the facility cryogenic grating spectrometer onboard the Kuiper Airborne Observatory. An efficient criterion of lasing is elaborated using a set of nonlasing, spontaneous emission lines as a reference. The shortest wavelength line showing an excess of radiation in our search is H10(alpha) at 52 micrometers . We briefly discuss possible reasons for the lack of detectable lasers in the visual and near- infrared domains.

Astrophysicists tell us that planetary systems are a byproduct of stellar evolution. This paper reviews the hazard human civilization faces from comet or asteroid collisions with the Earth, then makes the speculation that any ETI civilization evolving on any habitable planet would face the same sort of hazard from its star's residual protoplanetary debris. When the putative ETI civilization progresses to an active search strategy, radar and/or lidar signals used can result in a form of electromagnetic leakage radiation. Thus, the SETI programs of various radio and optical astronomers should evaluate the detection probabilities for signatures of the transient lidar or radar beams likely to result from an ETI civilization's active debris search technology.