UFOs or flying saucers or whatever believers are calling them now, are ENTIRELY a creation of the English language communications media. People hear about other people seeing strange things in the sky, go out and look, and see strange things too, because ANYTHING in the sky is strange to them. And since the media blitz is in English, the folks reporting the UFOs are mainly in English-speaking countries.
Looking only at the US, we see UFO sightings are largely confined to regions where people "follow the news," and have very little opportunity or motivation in general to look at the sky, day or night. The very first extensive US sightings of "mysterious objects" in the sky date to the late 19th Century when there was very extensive newspaper publicity about inventors testing powered balloons, and a wave of sightings of such "airships" occurred all over the USA, despite the confirmed fact that there were no such airships in the sky to be seen. But the modern UFO craze began in 1947, and has continued until the present day, marked by what the USAF used to call "flaps," periods when there is a peak in media publicity about "strange sightings," naturally leading to huge numbers of reports of such sightings.
UFO mythology has been around now for more than 75 years, and about the only legacy is the many people still reporting seeing things in the sky they don't recognize, almost always at night. The queen of these reports is the planet Venus, which puts on an incredible display when low on the horizon after sunset or just before sunrise. But Mars and Jupiter are strong runners up, along with meteor fireballs and lights on aircraft. But we shouldn't forget the many UFO photos taken in those 75 years, almost all taken in daylight. These were often pretty impressive in the early days, when the UFO was kept realistically far from the camera. Now computer generated images have ruined the whole genre. As I realized back in the 1950s as a teenager, the UFO craze was science fiction come to life! But it violated every bit of knowledge of physics and astronomy existing at the time, or existing today.
Below are some photos taken for homework by earlier students in the class, Physics 341, Pseudoscience. All photos were taken with regular film cameras, on Kodak color film, and processed and printed at local drug stores. No photo manipulation of any kind was done.
Yet, completely absurd and ludicrous images like the ones below are accepted as "authentic" photos of real UFOs by firm believers.... This reduction to absurdity is found in all pseudosciences... there are no boundaries and there is no input sought from any aspect of reality... the audience for the material is seemingly endlessly gullible.
A classic example of synergy is that the blitz of publicity about flying saucers in 1947 - 50 caused an explosive growth of interest in the genre of popular fiction known as "science fiction." It was first seen in semi-modern form in the pulp magazines of 1920 - 1949, but a revolution in the publishing of paperback original novels, beginning in 1950, and a simultaneous explosion of movies with science fiction themes, also beginning in 1950, made one particular plotline that was exceedingly common, the visitation of our planet by creatures from other worlds, into an almost inescapable stereotype of popular culture. It was therefore almost guaranteed that the most popular bogus "explanation" for UFOs was that they were spaceships from another planet, probably a planet in another solar system! Thus the most improbable of all "explanations" became the standard scenario.