A few years ago, I came across a site that proclaimed grandly: "Amateur Science Solves the UFO Mystery". The anonymous writer of this paper takes the old hypothesis that UFOs are atmospheric mirages and carries it a step further, claiming that UFOs are mirages of stars or planets. While there are many flaws in the paper's application of this hypothesis to specific cases, the main hypothesis is worthy of scrutiny.

What are "atmospheric mirages?" Well, all mirages are atmospheric mirages. Mirages are not images of nonexistent objects; they are images of objects that are real, but are just not where they seem to be. The reason these objects appear to be where they are not is because the light rays that make up their image are bent, or refracted from their normal straight line path. The refracting occurs because cooler air is denser than hot air. When the light rays from an object hit the boundry between the layers of air of different temperatures, they are refracted upward or downward from their normal path. An observer who is at the proper angle in relation to the image and the refracting boundary will then see an image of the object above or below the object's true location.

There are different types of mirages. Have you ever seen what appears to be water on the highway ahead of you on a hot summer day, that vanishes when you get closer? That's a type of mirage called an inferior image, and what you're actually seeing is an image of the sky itself. The light rays of the image are bent toward your eyes by the boundary between the layer of very hot air next to the pavement and the cooler air above it. The mirage of a lake in the desert is formed in the same way. The image of the sky is refracted so that it appears to be on the sand, thus appearing to be a lake in the desert.

Another type of mirage is known as a superior image. In this type of mirage, which usually occurs over water or ice, the light rays from an image are refracted downward rather than upward. As a result, a ship on the ocean may seem to be floating in the air. Also, an object that is below the horizon, that could not normally be seen, may be seen on or just above the horizon. This phenomenon is called looming. The image may also be magnified, so that very distant objects may seem closer.

A very special type of superior image mirage is one called a fata morgana. This mirage sometimes appears to be a castle or a city floating on the sea. This type of mirage is one that can only occur where there are alternating layers of warm and cold air near the surface of the water. This creates a very strange image of a distant object that is actually a combination of several images of the same object. The fata morgana mirage is named after Morgan La Fay, the enchantress who was the half-sister of King Arthur. She was something of a siren who supposedly lived in a castle under the sea, and was said to sometimes make this castle appear reflected up in the air, to lure unsuspecting sailors to their deaths. The most famous fata morgana appears in the Straits of Messina, between Italy and Sicily. They are also sometimes seen on the Great Lakes, and can sometimes occur over ice in Alaska and at the poles.

So, is this the "solution to the UFO Mystery" or not?

Well, superior images rarely appear more than a degree or so above the horizon. The necessary layers of warm and cool air tend to form bands that are parallel to the Earth's surface, so the light rays, which must hit the inversion layer obliquely, will not be refracted if the source object is high in the sky. So, the only UFOs seen by a ground observer that might be explained this way would be those that appeared just over the horizon, that could be a refracted image of something just below or just above the horizon.

What about the amateur scientist's idea that UFOs are the refracted images of stars and planets such as Venus or Jupiter?

Well, again, if the star or planet is just below or just above the horizon, then a slightly magnified superior image of it might be seen slightly above the horizon. It certainly happens with the sun. If you're in the right place at the right time, you can even see the sun set twice. First the real sun sets, then a superior image of it appears and sets. But if a UFO is seen high in the sky, then this explanation won't work. The layers of warm and cool air necessary to create the mirage are more or less parallel to the ground. As the field of view moves upwards from the horizon, the alignment of viewer, object, and refraction layer is lost, and no mirage will be created.

The problem with mirages as an explanation for UFOs, even most of those seen near the horizon, lies in the descriptions of UFO movement. Mirages don't zoom around the sky at speeds faster than conventional aircraft. A mirage can have movement if the real object is moving, so a mirage of a ship on the ocean will move at the same speed that the ship itself is moving. If the layers of warm and cool air that create the mirage move, then the mirage would move up and down slightly. But that "slightly" is very slightly. It's not going to appear to move across several degrees of sky, and it certainly isn't going to fly over the observer's head.

The mirage "explanation" for UFOs was a favorite of the astronomer and UFO debunker Donald Menzel years ago, with as little success then as now.

This article was previously published in 2000. It has been revised slightly by removing dead links and adding new ones as needed.

Print References: • UFOs: A Scientific Debate, edited by Carl Sagan and Thornton Page A collection of evidence and opinion from both sides.