ASTR 1210 (O'Connell) Study Guide 18

Poster from a 1957 movie featuring all the earmarks of the classic invasion
drama: flying saucers, death rays, and big-headed, bug-eyed aliens
with triangular faces and a penchant for scantily-clad women.

Because it fixes the ultimate scope of the human universe by exploring the largest scales of space and time, astronomy has always had a strong hold on the imagination. Inevitably, discoveries about stars and planets raise questions about life on other worlds.

Speculation about inhabitants of other planets goes almost as far back in history as there are written records, but it was given new impetus after 1550 by the enormous Copernican/Galilean universe, which was potentially infinite in extent and possibly filled with planets like the Earth. This idea was championed by early post-Copernican writers like Thomas Digges and Giordano Bruno.

Until the end of the 19th century, aliens were usually imagined to be enlightened and benevolent creatures. Since then, the popular concept of aliens has darkened considerably. As the movie poster above vividly testifies, they are now typically viewed as menacing (the Steven Spielberg cutie-pie creations in "ET" and "Close Encounters of the Third Kind" notwithstanding).

The change can be traced to a single novel, stimulated in turn by astronomers' studies of the planet Mars. This lecture discusses the novel and one of its main legacies: a remarkably widespread form of mild mass hysteria, the "UFO" phenomenon. "UFO's" lead us to return to the subject of the standards of scientific evidence and interpretation of observations.

Martians rule the British Navy in "War of the Worlds"

A. The War of the Worlds

Claims of some astronomers (1875+) to have detected Martian "canals" and Percival Lowell's widely circulated arguments that these were artificial and were built by civilizations on Mars provoked intense public interest in the possibility of extraterrestrial life.

Intrigued by the notion of life on Mars, the English writer H.G. Wells -- already a well-known author of "scientific romances" like The Time Machine and The Invisible Man -- conceived the novel The War of the Worlds (1898).


Intrepid junior scientist David notices something's wrong in the backyard in this comic-book promo for the film "Invaders from Mars," a classic 1950's paranoid fantasy in which his parents and most other adults are taken over by the invaders, except for a dashing astronomer and a beautiful doctor, who help David save the world---or do they?

B. UFO'S and the Limits of Science

Another lasting legacy of Lowell, Wells, and a vast amount of speculation by others is the "UFO" controversy. What started as a legitimate (if mistaken) interpretation of astronomical observations and a brilliant piece of fiction has become a worldwide mini-industry, with a multitude of committed believers and its own media and interest groups, not to mention millions of web sites. It is based on the belief that the Earth is under continuous surveillance by alien spacecraft and that there is a government conspiracy to cover this up.

"UFO" is an abbreviation for "Unidentified Flying Object"

UFO reports

Who reports UFO's?

UFO reports have many historical precedents.

The modern era of UFO's began in June 1947 with widespread media coverage of a report that civilian pilot Kenneth Arnold (at right) had seen a formation of "saucer-like" aircraft flying at speeds over 1000 mph near Mt. Rainier.

Anomalistic phenomena

UFO's are an example of an anomalistic phenomenon: something apparently inconsistent with the prevailing scientific consensus but only marginally documented.

Where do anomalistic phenomena fit into the scientific context? And under what circumstances should we accept them as expanding the boundaries or limits of conventional or mainstream science?

Consider mainstream science first:

Varieties of pseudo-science


In contrast to the subjects of mainstream science, "anomalistic" phenomena are not even established as real. There is insufficient objective, controlled evidence to show that the claimed phenomena even exist, let alone imply something beyond the capacity of normal science to explain.

Most pseudo-science is harmless, except for the sloppy thinking and miseducation it encourages. But some pseudo-science poses tangible threats to you and society. For example:

The role of credulity

The widespread interest of the public in anomalistic phenomena is fueled by human credulity: the proclivity to believe things in the absence of good evidence because they appeal to personal prejudices. This is a form of what psychologists call confirmation bias.

Scientific standards

How should UFO reports be interpreted in a scientific context? How much credence should be given to the extraterrestrial hypothesis?

Scientific assessment of UFO reports

The bottom line is that in 75 years there has not been a single UFO case meeting the conventional standards for scientific validation as a new phenomenon, let alone the higher ones needed to accept an extraterrestrial interpretation.

Military videos and investigations (2004- )

Several extended videos of UFO's taken with US Navy aircraft imaging systems over the period 2004-2019 were released to the public starting in 2017 and generated great interest. These included radar and infrared data. The videos appeared to show strange structures and motions that were beyond the capabilities of known aircraft.

The Director of National Intelligence prepared a confidential summary of these and other cases (now relabeled "Unidentified Anomalous Phenomena" rather than "UFO's") for the US government and released a brief unclassified version to the public in June 2021. This was not very helpful. It did not reach firm conclusions about most of the 144 incidents reported but recommended in view of possible national security concerns that better reporting protocols were needed.

The combat systems involved here employ sensors and complicated processing electronics and software that aren't necessarily well designed for determining the intrinsic properties of the targets detected. They are vulnerable to various kinds of artifacts and anomalies. Researcher Mick West has analyzed the three most widely viewed videos and found reasonable explanations for them that don't involve adversarial or extraterrestrial aircraft, rather ordinary aircraft or balloons viewed from a rapidly moving platform and camera equipment that can produce artificial motions in the images.

Because of the intense revived interest in "UAP's," NASA convened a special advisory committee to establish an empirical agenda for investigating them in 2022.

In March 2024, the Defense Department released a more strongly-worded report stating unequivocally that there was no evidence in its records or studies it sponsored that UAPs are extraterrestrial spacecraft. As summarized by the Washington Post, "They were 'ordinary objects and phenomena and the result of misidentification,' sometimes by well-meaning witnesses who thought they had spotted something otherworldly." The Post itself interviewed some of the people who claimed they knew about captured alien spacecraft and reverse-engineering attempts by the US military but stated, "[We] chose not to publish these accounts because the individuals provided no evidence to corroborate their claims. Their information was almost exclusively based on second- or third-hand statements, usually from people the interviewees declined to identify."

Needless to say, coming so late (75 years) into the modern UFO era, this report will not be warmly greeted by the UFO enthusiasts and conspiracy buffs.

Watching the sky

Here's a simple reality check if you see something strange in the night sky:

  1. Watch for 5 minutes. Is the "UFO" stationary with respect to the stars? If yes, then it's probably a celestial object, a minimum of many millions of miles from Earth.
  2. Is it within about 40o of the western horizon (near sunset) or eastern horizon (near sunrise)?
  3. Is it in a Zodiacal constellation?

      If yes to all three, then it's probably Venus.
      Jupiter is also a commonly-reported "UFO," but it need not meet criterion (2) here.

  4. If it's a slowly moving light or cluster of lights, it's most likely an aircraft. Aircraft normally move across the sky steadily in straight lines from horizon to horizon. Lights are normally white and blinking, although they can also be steady and sometimes red or green. Higher altitude aircraft may not make any detectable sound. As they approach their destination airport, aircraft will turn on very bright landing lights, which will definitely look strange if you are unused to them.

      Ordinary spacecraft, including the International Space Station, can occasionally be seen for an hour of so after sunset or before sunrise, when they are still out of Earth's shadow at their altitude. They will move silently in straight-line paths. Bright temporary flares or "glints" can occur as sunlight reflects from the surfaces of some satellites.

      The Heavens Above website specializes in tracking satellites and satellite flares and can predict their appearance for any place on the globe.

For help in placing UFO reports in context, you might refer to the guides published by the Center for Inquiry and their list of seven tips for keeping reports grounded in reality.


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Last modified March 2024 by rwo

Artwork here is from War of the Worlds, The Musical and original film posters & promo material. Scan of the cover of the 1993 edition of WoW from Dr. Zeus. Text copyright © 1998-2024 Robert W. O'Connell. All rights reserved. These notes are intended for the private, noncommercial use of students enrolled in Astronomy 1210 at the University of Virginia.