Conspiracy theories often rely on arguments that take the following form: “Because there is a mystery with no ready explanation, this means that things are not as they seem; there is a hidden reality, which I can explain.”

Perhaps the most well known supposed mystery surrounds the Moon landing in 1969. The American flag that the astronauts planted appeared to be rippling in the wind – but there’s no wind on the Moon, so how could this have happened? Conspiracy theorists used this mystery as “evidence” that the entire event must have been staged in a studio on Earth.

Instead of an elaborate charade, there is a very simple explanation for why the flag appeared to flutter in the breeze. NASA didn’t want the flag to hang limply, so it constructed a telescoping, horizontal bar to which the top of the flag was attached. When the astronauts deployed the flag, they could not get this bar to extend fully. This caused a kink in the flag, which made it appear to be rippling in the wind. Later crews left the flag like this because they liked the way it looked. Conspiracy theorists took this mystery, which had a very simple, but not well known, explanation and presented it as “proof” that the moon landing never took place.

This technique of pointing to supposed mysteries can be surprisingly effective. It may be that our minds are especially attuned to look for anomalies, perhaps as a sign of danger. This may have been very useful for survival in the wild, but is not very useful for understanding our complex, largely man-made world. Most apparent mysteries can be explained if one does the necessary research.

Robert Cialdini’s classic book Influence: Science and Practice summarizes very interesting studies by University of California sociologist David Phillips that demonstrate how suggestible people are.

Philips examined U.S. suicide statistics from 1947 to 1968 and found that within two months of a front-page newspaper story about a suicide, an average of 58 more people killed themselves, primarily in that part of the country where the reported suicide had occurred.

After actress Marilyn Monroe was found dead from an overdose of sleeping pills in 1962, there was a 12% increase in suicides by overdoses in the following months.

Philips also found that when news stories reported the suicide of a young person, there was a subsequent increase in fatal car accidents (which may have been intentional) involving young people. When the suicide of an older person was reported, more older drivers died in car crashes.

These apparent “copycat” suicides demonstrate the power of suggestion, which is also apparent in the history of sightings of UFOs – unidentified flying objects.

A recent article on the history of UFO sightings notes that private pilot Kenneth Arnold was the first person to report a UFO sighting, in 1947. Arnold said that he saw nine airborne objects that flew “like a saucer if you skip it across the water.” Arnold never said the UFOs looked like saucers; he said they looked like boomerangs. But “flying saucers” is what stuck in people’s minds and soon there were many sighting of “saucers” around the world.

One wonders if the power of suggestion was at work in these “flying saucer” sightings. If news of suicides can cause people to kill themselves, news about “flying saucers” may be enough to encourage people to see them.

The March 2009 issue of Popular Mechanics magazine has a special feature on the science behind sightings of UFOs – unidentified flying objects.

It says many UFO sighting are caused by military aircraft on training flights – or flares they drop.

Popular Mechanics shows six U.S. military aircraft likely to be mistaken for UFOs. It notes that the “flying wing” B-2 bomber “looks like an alien craft from nearly any angle and specifically like a flying saucer when viewed head-on or in profile.”

The magazine gives several examples of alleged UFO footage. In one, a mysterious ring of bright lights over Phoenix, Arizona in 1997 was caused by decoy flares a pilot had dropped.

Others are hoaxes. In March 1983, more than 300 people reported seeing V- and boomerang-shaped lights in New York’s Hudson Valley. Pilots had rigged their planes with extra lights before flying in formation at night.

Styrofoam plates and bowls were used in another hoax photo.

Some UFO sightings may be caused by natural phenomena, like the large saucer-shaped lenticular clouds that can form near mountains.

The planet Venus was mistaken for an enemy aircraft in World War II and fired at.

As Popular Mechanics points out, belief in flying saucers is a distinctly modern phenomenon. In the ancient past, people thought gods rode chariots across the sky. Our fantasies are now more technologically advanced.