As an astronomer, I have been asked countless times if I believe in UFO's. The questions are usually posed in a challenging sort of way, because on most instances, the questioner already was a firm believer in spacecraft and little green men. Perhaps because astronomers watch the skies, we are supposed to be an expert on all aspects of the sky, ufo's included!

 UFO sightings fall into 3 general categories, hoaxes, natural phenomena and all others. Only a small percentage of UFO sightings are hoaxes, but they are usually the most dramatic, the best covered, and often lead to books and appearances by the person who made the ?sighting.? A well done hoax can generate quite a bit of money.

 The majority of UFO sightings fall into the natural phenomena category. They are usually made by honest people who mistake an object or weather event  for a UFO. Planets, twinkling stars, weather balloons, airplanes, clouds and even birds have been mistaken for visitors from another world!

Once the hoaxes and natural phenomena have been discounted, what remains is "the others." There are only a  few of these type, ones that cannot be explained easily but appear to be honest reports. Some of these are reports that are passed along, each time getting just a little more interesting. Like the old game of ?whisper down the lane,? the end story is quite different from the original report!

Another explanation of the remaining sightings is the old psychological tendency to see what we expect to see. People who read about UFOs are far more likely to report one. That person may see a meteor, mistake it for a spacecraft and their subconscious does the rest. . Our brains are very good at filling in detail that fit the pattern of the object we think we see. It is a perfectly normal thing for the brain to do, but at the same time, we need to be rational about just what we see. It is quite possible for an honest person to describe something they saw in such a manner that it cannot be explained as natural phenomena.

Numerous groups of scientists have studied UFO reports over the past few decades. Not one study was able to find even one sighting that was conclusively a UFO. Thus there is no evidence for the existence of alien visits. But UFO buffs are a die hard bunch, the next claim they like to make is ?cover-up!?

These UFO die hards claim a large conspiracy between government, military and scientists. The conspirators are supposed to be covering up anything from actual photographs to spacecraft to alien remains. They fail to accept that the government is not good at covering up much of anything, even when there is only a few people involved!

I don't mean to sound like a pessimist. In fact, I strongly believe that there is a high probability of extraterrestrial life. We have already found planets orbiting other stars, it seems quite natural that there would be life on some of them. I think a visit from neighboring intelligent life forms would be an incredibly wonderful event, no doubt one that would change humanity forever. But reality calls, presently there is no evidence that little green men have ever buzzed our planet!