A unidentified flying object is just that—a flying object that has not been identified. There need not be evidence of alien hi-jinx.

My criteria for a credible UFO report would include:

  • Verified by authentic photographic evidence or several eyewitness reports.
  • Insufficiently explained by natural or human-caused phenomena.
  • Furthermore, such an explanation must not be scientifically suspect, and also must be substantiated. There probably could be a reasonable explanation for all such events, but there must be some underlying evidence that the stated cause was, in fact, in effect at the time. For instance, if it is explained by some human-made aircraft, there must be evidence that such aircraft was flying in the vicinity of the sighting.

Of course, as reasoned skeptics, you are free to apply any criteria you deem relevant.

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    I don't understand your third criterion. Why ask for evidence to identify flying objects when you're specifically looking for unidentified ones? Commented Mar 13, 2011 at 0:35
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    there's no evidence whatsoever that ufologists will accept that invalidates their wild claims. Therefore your 3rd criterium is impossible to meet.
    – jwenting
    Commented Apr 20, 2011 at 8:28
  • 2
    There used to be a wonderful, but anecdotal, answer to this question here. It's been (quite reasonably) deleted, since it had no references, but it can be read in the wayback machine.
    – Bobson
    Commented Sep 11, 2015 at 1:26
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    Voting to close as off topic. This question does not identify a notable claim to challenge. Also the last paragraph makes it rather opinion based. Commented May 17, 2020 at 9:19
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    "A unidentified flying object is just that—a flying object that has not been identified. There need not be evidence of alien hi-jinx." In that case, this is a trivial "yes". I suspect that, at some point, every single person reading this has seen a flying object and not known what it was, which is to say that they could not identify it. Commented May 17, 2020 at 10:37

5 Answers 5


No UFO has ever been revealed to be an alien spacecraft. That said, we can't explain all UFOs through natural phenomena. In some cases the sightings remain mysterious.

From 1947 to 1969 a project called "Blue Book" was run by the USAF to investigate UFO sightings. The results are the following:

From 1947 to 1969, the Air Force investigated Unidentified Flying Objects under Project Blue Book. The project, headquartered at Wright-Patterson Air Force Base, Ohio, was terminated Dec. 17, 1969. Of a total of 12,618 sightings reported to Project Blue Book, 701 remained "unidentified."
-- source

As such, I would say that, yes, unidentified flying phenomena that cannot readily be explained away are quite common, 1 every 11 days on average (in the United States alone).

You can now browse the Project Blue Book files online as they have been disclosed.

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    ++ It's really easy to generate UFOs. Just have something flying, and don't have enough money/time/interest to research it. I do sometimes enjoy watching History Channel shows where these people keep trying to sneak onto military bases, trying to expose what the government is hiding, which could, by implication, be alien spacecraft, else why would it be secret? Commented Mar 24, 2011 at 20:50
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    Any UFO that is positively identified as an alien spacecraft would cease to be a UFO :)
    – jwenting
    Commented Apr 20, 2011 at 8:26
  • Official FOIA source for the same document: archives.gov/foia/ufos.html (US National archives website)
    – jwenting
    Commented Apr 20, 2011 at 9:15
  • I have strong doubts that your argument that UFOs "are [=present tense] quite common, 1 every 11 days on average" is still valid. Project Blue Book had to work with what was technologically available from 1947 to 1969. I'd be shocked if a US agency could still get away nowadays with 5 percent unidentified flying phenomena.
    – Schmuddi
    Commented Sep 17, 2019 at 22:00

They are not flying and they are not objects.
But people saw them :)
(you can find a colection of reports of events in my site)

The events are more correctly called: UAP - Unidentified Aerial Phenomenon.

Because I've been always skeptic I studied this subject several years ago (during months),
and I concluded that two classes of UFO events can be physically explained. (edit add: I decided to offline the content because no one care to know what I found)
IMO they are just Aerial Phenomenons. If you are so skeptic as I am you will have to study what I've explained there.
I'm expecting some comments if you deny my view point and downvote.
(the physical papers that I've consulted in relation to ice crystals and contrails... will be included in the site in the future)

quote from "Pilot Survey Results” at NARCAP.ORG (the site is offline in the moment of writing)

This paper presents the results of a confidential aircrew survey presented to 298 currently rated and flying commercial pilots employed by a U. S. airline. Table 5

Results Related to Reporting One’s Sighting

Total number of pilots having seen a UAP . .. . 16 (100%)
Number who did report the sighting . . . . . . . . 4 (25 %)
Number who did not report the sighting . . . . . 12 (75 %)

If there are about 600,000 commercial pilots currently flying in the U.S.A. and 23 percent of them saw something they couldn’t identify this amounts to 138,000 witnesses.

colections of reports on UFOs:
COMETA report (French association) detail the results of a study by the Institute of Higher Studies for National Defense
COMETA_part1.pdf 23 pages
COMETA_part2.pdf 47 pages

UK gov. National Arquives, UFO files Files released in March 2011
NASA ASRS Database world's largest repository of voluntary, confidential safety information provided by aviation's frontline personnel, including pilots.
National Aviation Reporting Center on Anomalous Phenomena- NARCAP
Narcap: 300 cases analysed

a few selected cases:
Chicago O'Hare airport: Narcap report
Astronautics & Aeronautics July 1971 Unidentified Object in the ~South-Central U.S., July 17,1957
L'observation du vol AF 3532 1994, Coulommiers, France (more here)
Analysis of a Photograph of a High Speed Ball of Light Jul 16, 1988 - I clearly see a contrail where sunlight is reflected.
google search "Police Chase UFO over St. Atham, Cardiff", in UK 2008

The Scientists have been divorced of the UFO problem:
Society for Scientific Exploration: Report on a Survey of the Membership of the American Astronomical Society Concerning the UFO Problem: (1994) : Part 1 and Part 2

My viewpoint of the case reported by a military pilot in the page 9 of Cometa report (pag 7 of pdf), Mirage IV - UFO encounter, March 7, 1977:
Chaumont 48° 6'40.76"N , 5° 8'23.67"E
Luxeil Air Base 47°46'59.00"N ; 6°21'1.29"E

Not reported, but it is true:
No one noticed that the path of flight was in the directon of the Full Moon, South India, and the contrail was above Switzerland (cold atmosphere, no wind for sure at the time of the event). The contrail stood straight for long enough time and transported the light of Full Moon, below the horizon, to the cockpit.
Just check the images bellow, obtained with help of HPlanet - Home Planet software and Google Maps)

Physical explanation:
A contrail is made of ice crystals that in non turbulent atmosphere descend slowly exposing the bigger faces (frequently hexagonal) parallel to the ground (they go down like a large leave falling from a tree). The normal to that face oscilates around 8º max and they offer a continuous mirror for light that jump from crystal to crystal without leaving the contrail when light is injected along the longitudinal axis of the contrail. The total reflection in the faces are due to the low angle of incidence providing a 'natural low loss optical fiber'. And that was the case of this report. The pilots usually can not see the contrails made by their own jets. This case is an exception. The contrail was there in the right direction and the moon light (full moon) made the impossible: for brief moments the pilots saw the moon. Most of the UFO lights seen by night are made by some invisible contrail in the right direction to sunlight or, the less frequent moonlight, when the sun or moon are already below the horizon.

Position of full moon over South India at the time of the event. position of full moon over South India

Local path of the flight over France and Switzerland local path of the flight

At left two red points (zoom it) is the path of the Mirage over France/Switzerland and a large white stripe to mark the path of the moon ligth. at left (red points) the path of the Mirage over France/Switzerland and a large white stripe to mark the path of the moon ligth

Check the report of the pilot:

They noticed a brilliant light coming towards their Mirage from their exact right and on a collision course with them, and first thought it may be a jet fighter, but when they radioed to the ground control at Contrex?ville for reporting it and getting it identified, they learned that the ground radar showed nothing and that no other aircraft was known to be in that area. The ground controller asked them to check their oxygen, which indicates that he thought the pilots may be hallucinating.

The light appeared bigger and bigger as it approached their aircraft from their rear right. The pilot was flying at Mach 0.98 and made a turn to the right and then to the left to make sure the light was not a reflection of some sort on the cockpit. As he did these maneuvers, both of the crew could distinguish that the light was the front of a dark solid object. Despite the evasive maneuver, the unidentified object managed to stay exactly behind them for a few seconds, a very dangerous situation if the unknown object were to be hostile. The then object made a turn to the North-West at an estimated speed of Mach II, and went away to the left of the Mirage IV.

and reappeared 45 secs later to tease again the pilots.

In my oppinion this report of the pilots is credible. Also credible is the existence of the contrails, even if we can not see them by night time. Incredible, IMO, is the lack of imagination of the scientific community and others, that in the absence of a theory try to put down the testimonys, or waiting for help from some alien people.

By day time the testimonys are mostly correct but the physical explanation is based in the well known (in this moment I dont have the name in my head)... effect, and ....

They report 'objects' but they saw 'light'.
Find a suitable source of Light and a path thru the medium (atmosphere).

  • Let me know if you can not see the images I've included, because the computer I'm using has stored all passwords and I may be fooled. Commented Mar 25, 2011 at 15:57
  • the images load after you click some links
    – Jader Dias
    Commented Apr 14, 2011 at 19:27
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    @Jader Thanks. (Now I've updated the answwr to other link more actualized). As I'm not a natural english speaker I do not know if I said my ideas clearly in physical and english terms. Tanks for your feedback. Commented Apr 20, 2011 at 3:32
  • I was still awake at five o'clock in the morning and mistakes happen. I'm Portuguese and I think you are Brazilian and lives in Brazil given the timing of your comments. But what I like to know is whether it is easy to understand what I try to explain in my link. Obrigado. Commented Apr 20, 2011 at 11:44

Christopher Melon, a former U.S. Department of Defence employee, now on the board of UFODATA, and recipient of the National Reconnaissance Office Gold Medal and the Defense Intelligence Agency Director’s Medal, whose background includes:

At DoD, Chris served on a small committee that provided oversight of all DoD special access programs, in order to eliminate potential waste and duplication. The oversight included visits to Area 51 and other sensitive facilities. He also spent over a decade on the Senate Intelligence Committee, involved in oversight of NRO, CIA, NSA and other intelligence organizations. He became the first Congressional official to review all of the NSA’s compartmented programs.

Chris responded to a question a recent article as follows:

Q. Which credible UFO incidents have you found particularly impressive and convincing?

A. A few stand out in my mind. In November 1989, thirteen police officers and hundreds of other witnesses saw two silent triangular craft gliding over Belgium. This was the beginning of a wave of sightings there lasting well over a year. Ground and air radar data were acquired as well. The Belgian Air Force investigated the events in cooperation with a team of scientists and consulted with the US and NATO countries, but could not find a conventional explanation.

On the night of March 30, 1993, over a hundred witnesses in England, including police officers and military personnel, saw a triangular-shaped craft able to rapidly accelerate in seconds from a hovering position. The British Ministry of Defense stated that “none of the usual explanations put forward to explain UFO sightings seem applicable” and concluded that the evidence showed that “an unidentified object (or objects) of unknown origin was operating over the UK.”

Similarly, multiple police officers in Southern Illinois saw an object in January 2000 that looked and behaved very similarly to the Belgian and British UFOs. In fact, the Illinois police officers’ drawings of the craft are uncannily similar to the depictions of triangular craft produced by Belgian law enforcement officers a decade earlier, as well as many others since.

In 2006, pilots and airport personnel witnessed a disc-shaped object hovering over O’Hare airport for over five minutes, yet no government investigation was undertaken.

And, while most sightings have conventional explanations, I think it is stunning how many reports come in regularly to groups like MUFON, with impressive detail, including photos or videos. I often hear from skeptics, “If UFOs are out there how come nobody ever gets a video with all the smartphones around?” That is ignorant, it happens all the time!

In all though, I thought it was an interesting enough article to quote in response to this question, an article worth reading in its entirety.


Yes, the US Government has publicly acknowledged the sightings of "unidentified aerial phenomena", but did not speculate on what they were.

The US Navy publicly stated on September 11, 2019 in an interview with The Black Vault, a website that specialized in publishing declassified documents, that three videos purporting to be leaked military gun camera footage of UFOs, were in fact genuine gun camera footage depicting "unidentified aerial phenomena", but that they were not able to make any comments about what they were. Quoting from that article:

“The Navy has not publicly released characterizations or descriptions, nor released any hypothesis or conclusions, in regard to the objects contained in the referenced videos.”

  • Ha, we are going in circles here. This question was revived because a recent question about those "unidentified" videos raised. In short, just because the Navy didn't publicly release an identification doesn't make these particularly compelling examples.
    – Oddthinking
    Commented May 18, 2020 at 5:34
  • @Oddthinking The Navy officially referred to them using their modern jargon for UFOs. They might or might not be aliens, but they're officially UFOs.
    – nick012000
    Commented May 18, 2020 at 7:07

The definition of UFO, and UAP, in the question is not accurate. When Haines modified the term in 1980 to UAP he adapted the existing USAF UFO definition nearly word for word. The presence of the UAP term in the global conversation arises soley from its definition by Haines and its promotion by NARCAP of which Haines was a founding member. While the above question may appear open it is clearly biased and is being asked by someone who is unfamiliar with the terminology, the data, and dismissive of the study as a whole.

"An Unidentified Aerial Phenomena, UAP, is the visual stimulus that provokes a sighting report of an object or light seen in the sky, the appearance and/or flight dynamics of which do not suggest a logical, conventional flying object and which remains unidentified after close scrutiny of all available evidence by persons who are technically capable of making both a technical identification as well as a common sense identification, if one is possible.” (Haines, PP 13-22, 1980) https://www.narcap.org/blog/definition-of-uap

Notice the term makes no reference to aliens or their craft. The UFO definition doesn't either. The terms are being co-opted by believers and so-called skeptics in their arguments over the principle, cause, or sources of UAP reports

As for the question itself, the simple answer is yes. Enough data exists to offer this advisory for pilots and atc.


And to conduct preliminary analysis of flight dynamics of several profiles of UAP/Object.

A Preliminary Examination of the Flight Dynamics of Four Profiles of Unidentified Aerial Phenomena, UAP, Commonly Associated with Aviation Safety Incidents as Reported by Pilots https://www.narcap.org/blog/flightdynamicsofuap Ted Roe, NARCAP.org

  • The first parapgraph is confusing. UAP isn't defined in the question. UFO is. It isn't clear what you mean by "incorrect", because the OP defines what they mean by a term. (Since this question was asked, we demand notable sources, so we can use the original claimants definition, rather than th question asker's.
    – Oddthinking
    Commented May 17, 2020 at 5:12
  • Hello Rock Lobster, this question would not meet modern standards here at skeptics as you will see if you have a browse of the help center (ensure that you have plenty of free-time, it's not a quick read) and per se, it would be almost impossible to provide an answer which also fits the standards - not a bad effort though given the givens. Welcome, and enjoy the site. Commented May 17, 2020 at 11:45

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