So we have a theoretical stalemate.

"Any scientist will probably say there is life somewhere in the universe. They've found evidence - not proof - of life on Mars. It would be foolish to think we're the only intelligent life form in the universe," said Dr. Toby Owen, professor of astronomy at the University of Hawaii-Manoa.

"But because of the distances involved, it's extremely unlikely they would find us, and equally unlikely that they would be able to reach us."

If you've ever had a close encounter with a UFO, check your map of the heavens. Chances are that bright, silvery disc might be from outer space all right. It might be a chunk of meteor, a comet or most likely, the planet Venus.

"People usually don't want to believe that it's something that simple," said Peter Michaud, planetarium manager at the Bishop Museum.

"The most frequently observed UFO is the planet Venus. Or it might be a fireball - a bright meteor that flies, breaks apart and does all kinds of stuff."

"It's the folks who never look up at the sky who report UFOs," said Barry Peckham, an amateur astronomer and president of the Hawaiian Astronomical Society.

Their confusion is understandable, said Owen. "Police have chased Venus. Ships have shot at it, and if you're not used to seeing it, its brightness can lead you to think you're looking at a spaceship."

Comparing UFO witnesses to those at criminal trials, Owen said it's difficult to find two people who will agree about what they saw.

"The Kennedy assassination is one example. There were thousands of people watching; it was on film, but even with that, people were still confused about what happened."

With UFOs, he said, the confusion is even greater. "You're talking about something very unfamiliar that's over in a couple of seconds. Maybe they glimpsed something out of the corner of their eye but didn't get to look at it carefully."

He said that he once witnessed a rocket release, and got a call the next day about seeing an object "pulsating in the sky."

"Well, it wasn't pulsating," he said. "It was just floating serenely up there."

Owen said that meteors might be followed by blobs of material that burn upon entering Earth's atmosphere, resulting in a series of lights that might be mistaken for a spaceship. Or in the case of Venus, turbulence in the earth's atmosphere creates a kaleidoscope effect as light passes through it, causing the planet to appear to change colors.

"In cases where people report repeat sightings of flashing red and green lights, we know they're talking about airplanes," Owen said.

Most recently, a woman caller asked about newspaper reports about an object seen in the sky above Maui. "What that was was interesting scientifically," he said. But it wasn't of interest to UFO hounds. Instead, it was a small body in orbit around the sun, an old comet that had lost all its gases, and therefore, was behaving like an asteroid.

"We try to take these questions seriously and keep an open mind," Owen said. "I like these puzzles, finding out what's what."

Still, says Michaud, if astronomers tend to be skeptical about alien spaceships, it's because no astronomer has ever seen one.

"For all the time humans have been looking at the sky, there's never been a case of an astronomer seeing a UFO, which is a bit odd," Michaud said. "Scientists tend to be pretty curious. We always consider possibilities, and if someone were to see something, we'd want to know what it is, too."

Owen agrees, saying that as a child, "I wanted to see (UFOS) so I was always looking at the sky, but I was always finding some explanation for what I saw. I would love for it to be true."

When it comes to two inexplicable entities, government or UFOs, those who believe in alien craft prefer to side with the aliens than their fellow man.

"I don't like to see this paranoia that you see in newspapers on checkout stands," Owen said. "It's always about how government has a coverup or NASA has information that they won't release. The information is there and available to anyone who wants it."

The conspiracy theory just doesn't hold up, he said. "If UFOs did exist, they would be everywhere, not just in the United States. That would mean all governments, all around the world - including governments that don't get along - would have to get together and say, 'We're going to keep this secret.'

"If we were visited at the intensity which people report, it would be open knowledge by now. It just doesn't make sense. And the more TV shows there are, the more UFOs people see. There seems to be a connection," Owen said.

"It feeds on itself. Once somebody claims to see things, others come along. It's a well-observed phenomenon. We get pockets of activity, but they never have documentation. I'm sure that's what people would call a conspiracy. But if scientists saw something like this, they'd want to know about it too."

Believers can be very stubborn, even with no evidence to support their claims. Peckham said he often meets people who insist that there are structures built on the moon, but he said, "We have studied and studied the moon, we've flown satellites around and around it and taken pictures of every square inch of it.

"And amateurs who are not locked into any government conspiracies can look up and see there is no fortress on the moon," Peckham said.

Michaud said that most people are not skeptical enough. "People want to believe in not just UFOs, but pseudo-sciences like astrology. We need to have mysterious, wonderful things happening, but I think the universe is amazing enough. It's even more amazing than most of the UFO claims."