210
THE SEARCH FOR
INTERSTELLAR
COMMUNICATIONS
RADIO TELESCOPES
IN CONTEXT
KEY ASTRONOMERS
Giuseppe Cocconi (1914 –2008)
Philip Morrison (1915 –2005)BEFORE
1924 A “National Radio
Silence Day” is instigated
to tune in on any potential
Martian messages.1951 US physicists Harold
Ewen and E. M. Purcell detect
the 21-cm hydrogen line.AFTER
1961 Frank Drake formulates
the Drake Equation to
estimate how many intelligent
civilizations are likely to lie
beyond the solar system.1977 At Ohio University, Jerry
Ehman picks up a sharp signal
30 times the background noise
level. This “Wow! signal” has
never been detected again.1999 The SETI@Home
network uses the combined
power of millions of volunteer
desktop computers.I
n September 1959, the
scientific journal Nature
carried a short but hugely
influential article: Giuseppe
Cocconi and Philip Morrison’s
“Searching for Interstellar
Communications.” This introduced
an entirely new field of scientific
endeavor—speculation on the
nature of extraterrestrial life and
the possibility of intelligent beings
existing outside of Earth. For
the first time in scientific history,
alien-hunting had been framed
as a serious proposition.New radio telescopes
make it possible to look
for messages in the
radio spectrum.The 21-cm wavelength
emitted by hydrogen
atoms in the radio
band is the same
across the universe.Start the search for interstellar
communications at this wavelength.If there is other intelligent life in the universe,
it may be trying to communicate.The completion, in 1957, of the
250-ft (76-m) Mk 1 radio telescope
at Jodrell Bank in England—just
in time to track the world’s first
artificial satellite, Sputnik 1—had
brought new possibilities into
focus. If equipped with a powerful
transmitter, this kind of telescope
was capable of communicating
across interstellar distances with
any civilization that had managed
to achieve the corresponding
technology. Cocconi and Morrison’s
paper argued that, on some planet
orbiting a distant star, advanced