As was true with other early civilizations, the early Greeks viewed the earth as the center of the universe. Aristotle (384 to 322 B.C.), in summarizing the best Greek understanding, claimed that all earthly material was composed of four elements: Earth, Water, Air, and Fire. And the heavens were composed of an entirely different fifth element: Æther. With such understanding, the only conceivable place for life was on Earth although our ætherial souls might float up to heaven or down to the underworld after our death. All heavenly objects including the Sun and Moon and other wandering planets circled about the Earthly inhabitants daily.
After measuring the Sun to be larger than the Earth, Aristarchos of Salmos, (f 280BC) proposed that perhaps the Earth might actually orbit the Sun. But the Greeks could find no observable evidence to support that proposal. Only because Nicholas Koppernigk (he Latinized to Copernicus, 1473-1543) considered the elaborate heavenly system of Claudius Ptolemy of Alexandria (87 -150 AD) contained imperfections and non-circular motion did he reconsider Aristarchos proposal and introduce a solar system with exclusively perfect circular motions. The Copernican System was largely considered an unreasonable curiosity until newly calculated tide tables based on it proved to be more accurate than badly outdated tide tables based on Ptolemy's model. From an intellectual view point, Johannes Kepler (1571-1630 below left) discovered that Copernicus' spacing of the planet orbits miraculously fit the geometry of the five only known perfect solids. About the same time Galileo Galilei (1564-1642) constructed an early telescope and noticed imperfections in the form of spots on the Sun, moons that orbit Jupiter and not the Earth, and what appeared to be mountains and valleys on the Moon similar to those on Earth. Suddenly it seemed plausible that the Earth was a mere planet just like the other known planets. And if that were true, perhaps those planets might also have life much like that on Earth.
75 years before Newton proposed universal gravity, Kepler came close to suggesting that concept in his Astronomia Nova. Over the last 20 years of his life, Kepler wrote and from time to time added notes to the Somnium, which some consider the first modern science fiction. Published incomplete after Kepler's death, the book describes an Icelandic boy who, on returning from studying with Tycho de Brahe on the Isle of Hveen, is treated by his mother to a supernatural journey to the Moon. Kepler describes the protection needed to survive the initial shock (acceleration) of the journey, immense cold and inhibited respiration, and reaching a point where attraction to Earth is balanced by attraction to the Moon (zero gravity) before being pulled down to the Moon. Kepler describes how there are different creatures and life forms on the Moon adapted to more extreme temperatures caused by the twelve times longer days and nights. Kepler even describes tides on the Moon caused by joint attraction by the Sun and Earth! The reduced gravity on the Moon results in taller mountains, plants, and other creatures. The temperature extremes effect life spans, skin coverings, breathing, and life styles.
Three and a half centuries later, German development of rocket weapons during World War II led after the war to use of rocket propelled missiles to orbit satellites. This allowed scientific research above the atmosphere looking outward towards space and downward gaining expansive views of Earth. In 1961 President John F. Kennedy challenged the United States to land a man on the moon by the end of the decade. While astronauts found no life on the Moon, there was much increased interest in possible extra terrestrial life. Claims for spotting unidentified flying objects, UFOs, increased dramatically.
In 1959 Philip Morrison and Giuseppe Cocconi were young physicists at Cornell University interested in gamma rays. Morrison recalled that
One spring day in 1959 my ingenious friend Giuseppe Cocconi came into my office and posed an unlikely question: would not gamma rays, he asked, be the very medium of communication between the stars? Morrison agreed that gamma rays would work, but suggested they should consider the entire electromagnetic spectrum for its possibilities. The result of this brainstorming was a short two-page article, which was published in Nature in September, 1959. Entitled Searching for Interstellar Communications, it is now considered the founding document of modern SETI.
One of the few people to take extra terrestrial life seriously in the 1950s was Carl Sagan (1934-1996 at right with Ann Druyan, partner, 3rd wife). Deciding to become an astronomer at age 5, Sagan became a professor at Harvard and Cornell, bestselling writer, Pulitzer prizewinner, advisor for NASA and JPL designed satellites, and the world's leading evangelist of science. He became an expert in all aspects of life on earth and experimented to determine conditions that led to life on Earth in order to determine the chances of life elsewhere. Although calculations based on experimental evidence led Sagan to believed that intelligent life on other worlds is likely, he was relentlessly skeptical about claims that Earth has been visited by UFOs. In the early 1980s when few others thought the effort worth while, Carl Sagan, Bruce Murray and Louis Friedman created The Planetary Society to further space exploration and the search for extraterrestrial intelligence (SETI).
In the summer of 1967 Jocelyn Bell (at left with early radio telescope), student at Cambridge, was monitoring a new radio telescope, scanning the skies for signs of planetary emissions and quasars. Some unexplained scruff kept appearing in her charts. At first, Bell and her advisor, Tony Hewish, thought that the signal must be common Earthly radio interference, but they found the signal was coming from elsewhere in the galaxy. They noted this signal pulsated at precise regular intervals, 3.7 seconds apart. At the time nobody knew of any physical phenomena which could send a signal with such regularity. Researchers wondered if the source might be a transmission from an alien civilization? Only half jokingly they labeled the source as LGM-1, standing for the first detected little green men. Eventually the pulses were explained as emissions from rapidly spinning neutron stars. But the search for alien civilizations had become scientifically respectable. Individual astronomers began seeking time on radio telescopes searching for regular patterns which might indicate intelligent life elsewhere in the universe.
The search became institutionalized in 1992, 500 years to the day after Columbus landed in the New World, when two NASA searches were launched. One search of more than 800 stars thought possible to have inhabited planets used the 305-meter (1000-foot) radio telescope in the mountains of Arecibo, Puerto Rico, the largest dish in the world (shown at right). The second program began mapping the skies using the 34-meter dish in Goldstone in the Mohave Desert. Earlier congressional efforts to cut federal funding was adverted by the intervention of Carl Sagan, who met personally with an opposing Senator and convinced him that SETI was a worthwhile pursuit. The NASA searches were incomplete and short-lived. The cancellation of NASA's SETI program in 1993 created trying times for the SETI community. NASA's involvement did however completely transformed SETI. Compared to the frugal individualized efforts of previous searches, SETI became a professional enterprise conducted by experts using the most advanced technologies available. The scope and sophistication of the searches increased by an order of magnitude through NASA's involvement.
Various private organizations attempted to step in and continue SETI efforts. Since 1996 The Planetary Society has also been supporting a radio all-sky survey led by Dan Werthimer of U.C.Berkeley using the Arecibo Observatory. But unlike previous efforts it doesn't need to wait for highly-competitive and hard to obtain observation time-slots. Instead, it is permanently perched above the Arecibo dish, scanning whichever part of the sky the dish happens to be pointed at and moving through the sky with the rotation of the Earth. While this approach would not work for a targeted search, it is well suited for an all-sky survey.
An offshoot of this effort is the enormous SETI@home project. This is a pioneering distributed computing project which sends data packets to millions of owners of personal computers around the world who wish to participate in the search. When their computers are not occupied by other tasks, a screensaver program analyzes packages of radio data searching for patterns that might indicated extraterrestrial life. After analysis is completed the local computer sends back the results and is forwarded a new packet of data to analyze. When SETI@home founders were looking for a sponsor in 1998, the Planetary Society provided the needed seed money and remains the main sponsor. SETI@home uses the data collected by the stationary Arecibo receiver. Over five million personal computers have contributed over 22 million CPU years of analysis. SETI@home has become the Earth's largest computer project. It can analyze its data at a depth and detail impossible by other conventional approaches. If you are interested in SETI, have authority to control the programs on your computer, and wish to contribute, see instructions in Procedure #4 below:
Communicating technical information such as observations and findings is a skill used by scientists but useful for most others. If you need course credit, use your observations in your journal to construct a formal report.