THE ELECTRONIC JOURNAL OF
THE ASTRONOMICAL SOCIETY OF THE ATLANTIC
Volume 3, Number 11 - June 1992
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TABLE OF CONTENTS
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* ASA Membership and Article Submission Information
* History of the Ohio SETI Program - Robert S. Dixon
* The Hyades: A Star Cluster Rich in Myth and Astronomy
- Ken Poshedly and Don Barry
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ASA MEMBERSHIP INFORMATION
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HISTORY OF THE OHIO SETI PROGRAM
by Robert S. Dixon
The Ohio SETI (Search for ExtraTerrestrial Intelligence) Program
began with a strong impetus from NASA's Project Cyclops. The goal of
Cyclops - a paper study conducted in the early 1970s - was to assess
what it would take in terms of time, people, equipment, and money to
mount a large search for radio signals from interstellar civilizations.
The end result was a report which was widely circulated as a NASA
Special Publication, recommending a small array of radio telescopes
which would grow with time as needed.
During my Project Cyclops research, it became clear to me that
many theoretical papers were being written about SETI but no one was
doing any extensive actual searching. I also realized that we had
a large, fully operational radio telescope available at Ohio State
University (OSU) which was designed explicitly to search for new radio
signals in the sky. It had just completed the largest all-sky survey
of natural radio signals made up to that time. Coincidentally, this
telescope was also chosen by the Russian scientist Gindilis as the
telescope most suited for SETI, due to its unique surveying ability.
Although we had no money, we did have a crew of able volunteers
on hand. Faced with the alternative of ultimately turning off the
telescope and letting it rust away, we decided that we had a respon-
sibility to seize the opportunity which had been thrust upon us and
start a real SETI program. It did not take too much arguing to
convince John Kraus, Director of the OSU Radio Observatory, to allow
me to use the telescope for humanity's first full-time SETI program.
The Ohio State Radio telescope is larger than three football
fields in size and equivalent in sensitivity to a circular dish
52.5 meters (175 feet) in diameter. The beam of the telescope is
elliptical, being forty minutes of arc in the declination (vertical)
direction and eight minutes of arc in the right ascension (horizon-
tal) direction. This may be visualized by comparing it with the
size of the Moon, which is a thirty minutes of arc diameter circle
in Earth's sky.
The telescope surveys the sky by remaining stationary and allowing
the rotation of Earth to sweep its beam in a narrow circular path
through the sky once each day. After a few days of observation, the
beam is moved slightly up or down and the pattern is repeated. It
takes several years to thoroughly search the sky.
We went on the air in 1973, using an eight-channel receiver
system, originally constructed for twenty-one-centimeter (21-cm)
hydrogen line observations by Bill Brundage. Bill later went on to
become Chief Engineer of the ninety-meter (three hundred foot) radio
telescope at Green Bank (NRAO). Later still he was responsible for
preparing the Very Large Array (VLA) in New Mexico to receive the
faint VOYAGER 2 spacecraft signals during its flyby mission of the
planet Neptune in August of 1989.
The bandwidths of the channels ranged from ten to fifty kilohertz
(kHz), depending on their distance from the center frequency. The
output of the eight channels was plotted as wiggly lines on pen
recorders. The charts were laboriously searched for unusual signals
by graduate student Dennis Cole - now a contractor to the Jet Propul-
sion Laboratory (JPL) - and used as the subject for his master's
thesis in Electrical Engineering. This may have been the first
graduate degree ever awarded in SETI.
The search strategy chosen at the time was to explore in the
vicinity of the 21-cm hydrogen line, Doppler correlated to the
Galactic Standard of Rest. Due to the random motions of the stars
and the rotation of our Milky Way galaxy, signals transmitted at
the hydrogen line frequency (1420.4056 megahertz, or mHz) would be
received at somewhat different frequencies because of the Doppler
shift. To avoid this frequency ambiguity, we made the deliberate
assumption that any civilization transmitting at the hydrogen line
would offset their transmission frequency in just the right way to
remove all their motions with respect to the center of the galaxy,
which is the only unique reference point shared by all the galactic
inhabitants.
It was then up to us to offset our receiver frequency to
compensate for Earth's motions to arrive at this unique "galactic"
frequency. Because of our uncertainty about the galactic rotation
velocity (we measure it by observing the motions of the stars and gas
in our stellar neighborhood), we still had to search a total bandwidth
of several hundred kHz. A lot of chart paper was generated during
the two years this effort continued, but no recognized signals of
intelligent origin were found.
By 1975, a fifty-channel filter bank receiver had been borrowed
from Green Bank. Software for the already old IBM 1130 computer
had been developed by Professor Jerry Ehman - now Chairman of the
Mathematics Department at Franklin University - and me, to process all
fifty channels continuously. The software was sophisticated, with
many internal checks for false alarms and equipment malfunctions.
Each of the fifty channels was processed independently, and the
computer automatically removed the individual gain and baseline
variations of each channel.
A number of search algorithms were run simultaneously, including
searches for both isolated pulses and continuous signals which rose
and fell in intensity in just the predicted way (for a continuous,
narrowband signal) as they passed through the antenna beams. The
highly processed output data were printed every ten seconds for all
fifty channels. Signals the computer thought were "interesting" were
also flagged and saved on punched cards for later analysis.
The IBM computer was built like a battleship and ran without fail
for many years. Its operating system could run huge programs in a
tiny memory very efficiently. It was fast, even by today's standards.
Over the years, a few cold hydrogen clouds were found and huge
piles of computer printouts accumulated. There was no magnetic tape
drive or equivalent device available, so there was no way to record
all the data permanently in computer-readable form. Only the small
fraction of data represented by the "interesting" signals were
preserved in computer-readable form. Along the way, a small NASA
grant was received, which continues today.
Two types of unexplained signals were detected during this search.
The first kind is quite rare, with the best example being the "Wow!"
signal found in 1977. This name was unintentionally applied from
Jerry Ehman's comments in the margin of the computer printout when he
noticed the signal. The signal was unmistakably strong and had all the
characteristics of an extraterrestrial signal. It was narrowband and
matched the antenna pattern exactly, indicating it had to be at least
at lunar distance. A signal from a nearer object would show a wider
pattern.
However, the strange signal was not coming from the direction of
the Moon or any planet, or even any particular known star or galaxy.
Of course there are always many distant stars and galaxies in the
beam of a radio telescope all the time, but that is not significant.
A check of artificial satellite data showed that no publicly-known
Earth satellites were anywhere near the position of the signal source.
Furthermore, the frequency of the signal was near the 1420 mHz hydrogen
line, where all radio transmissions are prohibited everywhere on and
off Earth by international agreement. We searched in the direction of
the "Wow!" signal hundreds of times after its discovery and over a
very wide frequency range.
We never found the signal again. It was gone. In fact, while
we were receiving this signal the first time, it turned off as we
listened. The radio telescope actually receives two beams from
the sky at once (somewhat offset in direction from each other) and
subtracts one from the other to cancel out terrestrial radio inter-
ference. Objects in the sky are usually received twice with a
slight delay, once in each beam. But the "Wow!" signal was received
only once, indicating either that it turned off after the first beam
received it, or that it turned on after the first beam had passed it.
What was the "Wow!" signal? Probably we will never know.
Conceivably it could have been a secret military satellite in solar
orbit, transmitting on an illegal frequency. Military transmitters
often ignore civilian agreements. Its characteristics rule out any
terrestrial transmitter, near-Earth satellite, reflection from space
debris, or equipment malfunction. Perhaps it was a transmission from
some other civilization. If so, it seems that they were not trying
very hard to attract our attention, since the signal disappeared
before we could really find out what it was.
The other kind of unexplained signals we receive are much more
numerous. These are narrowband pulses (lasting less than ten seconds)
which go "bump!" in the night. There have been thousands of such
signals received, apparently from all over the sky, and never from
exactly the same direction more than once. Clearly these signals are
not from any single source (intelligent or otherwise), but they are
very interesting in their own right. They could be some form of
previously unknown astrophysical phenomenon. As an example, pulsars
were first thought to be of alien origin when discovered in 1967,
due to their regularly timed radio waves. They are now known to
be rapidly rotating neutron stars, the remains of supernovae.
Of course pulsed signals like these could easily be caused by
terrestrial radio interference or equipment malfunction. But if those
were their sources, then they should appear randomly scattered across
the sky. The interesting thing is that they do not. They exhibit a
zone of avoidance along the galactic plane and areas of concentration
above and below the galactic center, along the galactic north and
south polar axes.
It is possible that the zones of avoidance and concentration are
caused in some complex unknown way by an interaction between the
galactic continuum radiation and the automatic gain and baseline
correction algorithms in the computer. We simply do not know. A
resurvey of a portion of the same area shows roughly the same effect,
so the phenomenon appears to be repeatable. We plan to resurvey this
area again with all new equipment in the future.
At one point, there was danger that the telescope would be
destroyed. The land under and around the telescope was sold without
our knowledge to a developer who wanted to enlarge the neighboring
golf course. The developer wanted the telescope torn down and
completely removed. This created a furor that was widely reported in
the world press. After great struggle and with help from many people,
the telescope was saved and a long-term lease was signed for the land.
For several years we published the first and only SETI magazine,
called COSMIC SEARCH. Its editorial board included all the worldwide
luminaries of SETI. The magazine was a technical and popular success,
receiving great praise on all fronts. Sadly, it was a financial
failure and finally folded after the thirteenth issue.
In the middle 1980s, a new and more powerful computer was donated
by Digital Equipment Corporation. We began what we knew would be
years of effort to place it into operation in the next generation of
the Ohio SETI Program. Unfortunately, while this development was
proceeding, the old IBM computer came to a premature death at the
hands of a mouse. The mouse had built a nest at the air intake to
the disk drive, cutting off the machine's air supply. This caused
the disk drive to destroy itself.
IBM said the computer was so old that it would cost a lot of
money to fix it. They also would not guarantee it to work normally
even after it was fixed. So regretfully we abandoned the IBM computer
and devoted all our efforts toward getting the new Digital computer
operational. During the years of eight-channel and fifty-channel
observations, we accumulated more on-the-air SETI observing time
than all earlier or contemporary SETI programs combined.
The new system (now in test operation) has many improvements over
the earlier one. No assumption as to exact signal frequency is made,
as the entire "water hole" (1.4 to 1.7 gigahertz, or gHz) is searched
continuously in three thousand channels. When a signal is found the
search is temporarily suspended, so that the signal may be examined
immediately in great detail and studied for an hour or so. We call
this the SETI ZOOM system, because of the way it seizes upon any
detected signal and focuses in on it.
This systems avoids the problem encountered by other SETI programs
where interesting signals are found after-the-fact as part of a
systematic search, but are no longer there when further observations
are attempted. Russ Childers has now written his masters thesis on
this system. An online catalog of known Radio Frequency Interference
sources has been developed, to be used by the computer to ignore them.
A new type of radio telescope is being designed and a small
prototype has been successfully tested. This telescope is called a
Radio Camera, since it forms an image of the entire sky at once.
This avoids the possibility that a signal might arrive from an
unexpected direction but be missed by radio telescopes that are
looking in "likely" directions. Jim Bolinger wrote his master's
thesis describing the prototype. Plans are now being made to build
a much larger one. Steve Brown is writing his masters thesis on
several aspects of this development.
We have named this the Argus telescope, after the being of Greek
mythology that had one hundred eyes and could see in all directions
at once. It is the physical realization of a concept that has been
fictionalized earlier by Carl Sagan in his 1985 book, CONTACT, and
by Arthur C. Clarke in his 1976 novel, IMPERIAL EARTH.
A new method of detecting unknown signals is being developed,
based on the Karhunen-Loeve transform. Unlike the Fourier transform
commonly used, this method makes no assumptions as to the type of
signal being received. It works well with all types of signals,
particularly so with complex ones. Professor Chuck Klein and his
students are running computer simulations of the signal detection
process, comparing the KLT approach to the FT approach.
The Ohio SETI Program has now been merged with the Canadian SETI
Program run by Bob Stephens. Bob is now at Ohio State University and
we are jointly figuring out how we can best combine our equipment.
This was made possible by a large increase in the size of our NASA
grant this year.
The Flag of Earth flies at the OSU Radio Observatory and many
other SETI locations around the world. It symbolizes the fact that
SETI is carried out on behalf of Humanity as a whole. The individual
people, organizations, and nations involved are but a part of the
incredible work being done to find intelligent life in the Universe.
Related EJASA Articles -
"Does Extraterrestrial Life Exist?", by Angie Feazel - November 1989
"Suggestions for an Intragalactic Information Exchange System",
by Lars W. Holm - November 1989
"Radio Astronomy: A Historical Perspective", by David J. Babulski
- February 1990
"Getting Started in Amateur Radio Astronomy", by Jeffrey M. Lichtman
- February 1990
"A Comparison of Optical and Radio Astronomy", by David J. Babulski
- June 1990
"Curbing Light Pollution in Ohio", by Robert Bunge - June 1991
"The Search for Extraterrestrial Intelligence (SETI) in the Optical
Spectrum, Parts A-E", by Dr. Stuart A. Kingsley - January 1992
"A History of Ohio's Perkins Observatory", by Earl W. Phillips, Jr.
- February 1992
THE HYADES: A STAR CLUSTER RICH IN MYTH AND ASTRONOMY
by Ken Poshedly and Don Barry
Consider the Hyades in the constellation of Taurus the Bull, an
open star cluster considered by most too big to be a telescopic object
and not quite bright enough to be a dazzling unaided-eye group from
urban skies. Binoculars best reveal this group's beauty, ranging from
the distinctly V-shaped bright stars which form the snout of the Bull,
Taurus, to the hundreds of dimmer cluster members in the vicinity.
The Hyades cover over five degrees of the sky. The total magnitude
of the cluster is 0.5, but with its individual stars so thinly
distributed, it seems less so.
The Hyades have been known variously by the Greeks, Romans, and
Arabs as Thyrene (or Thyene or even Thyone), Parilicium, Sidus Hyantis,
Al Mijdah, and Al Kilas. From ancient Greece to China, the Hyades
were associated with wet and stormy weather due to their seasonal
evening appearance in rainy November and disappearance in wet May.
In Greek mythology, the Hyades were the seven daughters of Atlas
and Aethra, making them half-sisters of the much more famous Pleiades,
another star cluster in Taurus. They were given the job of raising
the infant Dionysus (Bacchus), son of the god Zeus and Earthly
princess Semele. Zeus rewarded them for their good work with a
place in the heavens.
The classic V-shape outlines the snout and horns of Taurus. The
Bull's horns extend all the way to the star El Nath and a corner star
in the constellation of Auriga. The Pleiades mark the back of the
Bull: Perhaps these stars are stinging the Bull and goading him into
confrontation with Orion. Ahead of the V, a thin line of stars mark
Orion's shield, well placed to deflect the sharp horns. The middle-
left star, Theta 1 and 2, of the V is a lovely visual double, one of
the best wide equal pairs in the sky.
Today we know the Hyades to be the closest well-defined star
cluster to our own solar system. Although the cluster stars are young
(under one billion years), the cluster age itself is old compared to
many more familiar open clusters, which often disperse within tens of
millions of years of formation. The entire group is moving through
space relatively slowly - about fifty kilometers (thirty miles) per
second - toward a point several degrees east of the red giant star
Betelgeuse in Orion. Fifty million years from now, the Hyades and
other stars known collectively as the "Taurus Moving Group" will
appear as a dim telescopic object less than half of one degree in
diameter.
The Hyades distance from Earth, so important to our understanding
of more distant star clusters, was the subject of former ASA member
Edmund Dombrowski's Ph.D. thesis. His determination, based on
double-star observations in the Hyades, gives the most precise
measurement to date: Some forty-eight parsecs or 157 light years.
The age of the Hyades is inferred from the absence of bright, massive
stars, which burn up their nuclear fuel very rapidly and meet their
calamitous ends.
Several very important binary stars with relatively rapid orbital
periods are found in the Hyades. These stars are the best source of
knowledge about stellar masses and distances in the cluster and have
been studied extensively by Georgia State University (GSU) astronomers.
The star 51 Tauri was discovered to be a binary by Hal McAlister in
the late 1970s. It has an orbital period of 11.295 years.
Other notable binaries and their orbital periods are: Finsen 342
(6.277 years), ADS 3475 (16.3 years), ADS 3210 (27.672 years), and
ADS 3135 (89.470 years). Of these, only the last is resolvable in
an amateur optical instrument. Even then, with maximum separation
of 0.57 arc seconds, it is a test of superb optics and atmospheric
conditions for twenty-centimeter (eight-inch) and larger telescopes.
Historically, the Hyades distance was first determined through
what is now called the "moving cluster method". In this technique,
which works only for a cluster as close as the Hyades, the motion of
the cluster through space is apparent on exposures taken years apart.
The direction of each star is plotted, and when viewed as a whole,
appears as a series of arrows which meet at some location in the sky
toward which the cluster is moving. Only the Hyades are sufficiently
close that this motion and "vanishing point" is detectable in
exposures taken a few decades apart. A study of the relative velocity
of the cluster and the distance of its "vanishing point" gives an
estimate of the cluster distance, independent of the properties of the
stars themselves. Now, binary star studies can determine the distance
to individual systems within the Hyades to greater precision than the
moving cluster method, and most recent analyses of the Hyades distance
use these techniques.
Although observers often assume it to be a member of the cluster,
Aldebaran is much closer to us at only seventy light years distance.
Its ruddy orange color reveals its low surface temperature: Aldebaran
is a red giant star that just happens to be in the way. Every three
years, the planet Mars passes close to Aldebaran from Earth's view,
inviting comparison between the Red Planet and red "Eye of the Bull".
About the Authors -
Ken Poshedly was Secretary of the ASA through 1990-1991 and now
serves as the Publications Chairman. Ken has restored a Criterion
RV-6 Dynascope and is still clawing his way through the various
levels of "amateur astronomer" status. Ken is a long-time amateur
astronomer and maintains an ongoing interest in astronomical writing
and historical astronomy. Ken's interests also include education and
Volkswagens. A technical writer by profession, Ken has a degree in
Journalism from Kent State University in Ohio.
Ken is the author of the following EJASA articles:
"Did Kepler Fake the Evidence?" - May 1990
"When the Light Gets in Your Eyes, You Shouldn't Have to Drive
to the Country" - February 1991 (with James Smith)
"Solar Eclipses in History" - July 1991
"The July 11 Total Solar Eclipse and the ASA" - November 1991
Don Barry, ASA President, is an astronomer with the Center for
High Angular Resolution Astronomy (CHARA). Don is currently writing
his Ph.D. thesis involving measuring the relative luminosity of very
close double stars. Don's professional interests include optical
interferometry, binary astrometry and photometry, and innovative
instrumentation. An active amateur as well, Don's interests include
telescope making, antique instruments, and fostering amateur-
professional collaborations.
Don is the author of the following EJASA articles:
"Astronomy Week in Georgia" - August 1989
"Profiles in Astronomy: Albert Whitford" - September 1989; an
interview with Edmund Dombrowski and Sethanne Howard
"Alar Toomre: Galactic Spirals, Bridges, and Tails" - October
1989; an interview with Edmund Dombrowski and Sethanne Howard
"Observing the Wreaths of Winter" - December 1989
"The Mayall Four-Meter Telescope" - May 1990
"A Southern Travel Diary: An Observer's Tale" - August 1990
"Saturn's Great White Spot" - February 1991
THE ELECTRONIC JOURNAL OF THE ASTRONOMICAL SOCIETY OF THE ATLANTIC
June 1992 - Vol. 3, No. 11
Copyright (c) 1992 - ASA