Here are a number of stories about the three different types of UFOS: UAPs, IFOs, and TRUFOs. Don't know your UFO alphabet? Keep reading to find out what these acronyms mean.
CATEGORY 1: UNIDENTIFIED ATMOSPHERIC PHENOMENA
Unidentified atmospheric phenomena (UAPs) are UFOs that are produced by natural causes. 
Rather than being actual objects, some UFOs are simply strange lights, called "earth lights" by UFOlogists. These UAPs include earthquake lights (lights that appear before, during, and after earthquakes) and will-o'-the-wisps (fiery lights seen in marshy areas). According to author Paul Devereux, other earth lights are still unidentified but seem to be related to bodies of water, sources of power, and openings in the earth.
One somewhat common UAP has been identified as ball lightning. This phenomenon occurs very rarely, but it has been reported often enough that it now has a label. It looks like a round, glowing red-orange or blue ball and usually occurs when thunderstorms are near, though this is not always the case. It may make an unusual noise and be responsible for strange electrical happenings. In fact, it seems to form near electrical wires. In the air it may move quite rapidly, but near the ground it travels more slowly. It may explode, although it usually just disappears without a sound. Whatever it does, ball lightning is dangerous.
One case reported by astronomer and UFO investigator Walter Webb occurred on July 4, 1986, in Winchester, Massachusetts. It had rained lightly throughout that day, but then the sky turned darker and looked more threatening. At 2:20 P.m., Mrs. Domenica Falcione happened to glance out her kitchen window and spot a strange, red, glowing object hovering above some evergreen trees in her back yard. She was amazed at the sight and watched as the sphere remained perfectly still for perhaps thirty seconds. To make sure that her eyes weren't playing tricks on her, she turned away for a moment. When she looked back, the red ball was still hanging in the air.
Suddenly Mrs. Falcione heard an explosion, and her house shook. The burglar alarm and the automatic lawn sprinklers,began to work. She ran to the garage to check the meter box for the lawn sprinkler system; it was black and smoking, and the wall it was mounted on had been damaged.
In fact, the explosion had done a great deal of damage. A neighbor's tree had been blown apart. A foot-deep hole had been gouged below Mrs. Falcione's back fence. Her furnace and television set had burned out, and half of the fuses in the main fuse box were damaged. Altogether, Mrs. Falcione had to pay almost $2,000 to repair the damage.
An encounter with an alien UFO? Not quite. Astronomer Webb concluded that the culprit was ball lightning.
Another recurring UAP in recent years has been referred to by UFOlogists as mystery circles. These circles have appeared in fields, mainly since 1981, and although they have been observed in many countries, including the United States, they have been seen most often in England, usually between May and September.
The circles have been photographed for a recent book, entitled Circular Evidence, by UFOlogists Pat Delgado and Colin Andrews. The circles have many different formations. Most common are single circles, but sets of five are also found. None, however, are ever exactly alike. The only common denominator is that the corn or wheat crop is flattened but never damaged. Rather, the crop is swirled down to the ground.
What are these mystery circles?
Some people think that tricksters have selected isolated fields and mashed down the crop. As Delgado and Andrews have shown, however, the circles are flattened in a swirl and have different layers within the overall pattern. No footsteps are found.
A more plausible theory is that the circles are caused by a natural phenomenon known as a vortex, or whirlwind. Others believe that strong electromagnetic fields, deep in the earth may account for them. Either theory would help to explain why no two circles are the same, since wind currents and electromagnetic fields vary.
Still another theory is that the circles are created by spaceships. If UFOs are responsible for them, however, then each circle has been created by a different UFO quite unlikely, considering that thousands of circles have been found. Unless there are an equal number of different UFOs, at least some circle patterns would be repeated.
No one has been able to prove any of these theories, because no one has seen a mystery circle appear; they always seem to develop overnight. To make matters even more confusing, some strange events have been associated with them. People have had nocturnal encounters with UFOs only to discover the next day that a mystery circle has formed near the spot of the incident. And in at least one case, a configuration of circles was said to be related to a plane wreck.
On August 22, 1987, a set of four mystery circles was found in a cornfield near Winterbourne Stoke, England. Eight weeks later, on October 22, a British fighter jet flown by Pilot Humphrey Taylor Scott left Dunsfold Airfield on a solo test flight. Six minutes after takeoff, air traffic controllers lost contact with Pilot Scott and alerted other aircraft in the vicinity. The crew of an American military transport observed the fighter a short time later. What they saw stunned them: the cockpit canopy--and the pilot--were missing! The American plane followed the jet for about four hundred miles, until it crashed into the Atlantic Ocean.
What happened to the pilot? A day later his body was found in a field not far from Winterbourne Stoke. According to UFOlogist Colin Andrews, something had happened to Scott above the field with the four mystery circles. The jet apparently changed its course by a few degrees over the circles, a fact reportedly confirmed by the British Ministry of Defense. That's when the pilot left the aircraft, but the ejection seat was not found on the ground.
Although the Royal Air Force believes that Pilot Scott was manually ejected in a freak accident, Andrews is not so certain that the force that created the mystery circles could not also have removed the canopy from the jet, causing the pilot's death. Even though the circles were made two months before the incident, Andrews believes that the coincidence of the circles and the ejection of Pilot Scott is too great to be ignored. What do you think?
A final example of a UAP comes from UFOlogist Jennie Zeidman, who reported a strange experience involving a nightlight that a young doctor saw in Youngstown, Ohio, in June 1979.
Dr. Lynn Moorman was spending Saturday night at her parents' house. Whenever she stayed with them, she slept on the couch in the family room. The couch was set against a wall under a large picture window.
Around three o'clock that morning, Dr. Moorman opened her eyes and noticed a flashing light outside the house. She immediately thought that it was a firefly. A moment later, as the light continued to flash, she realized that it was too bright to be a firefly.
Then the light moved toward the window and-- unbelievably--through the windowpane into the room. It passed in front of her, perhaps as close as three feet. The light seemed as bright as a sixty-watt bulb. Then Dr. Moorman noticed that it appeared to have two sets of wires coming from the top and bottom.
Suddenly the family dog, who had been sleeping beside the couch, woke up and noticed the flashing light. Each time the object flashed, Dr. Moorman saw it clearly; but when the light turned off, the object was no longer visible.
Dr. Moorman was quite scared by now, even though the flashing light seemed to be unaware of her and the dog. She thought about screaming, but couldn't open her mouth. When the light moved into the kitchen, she ran to her sister's bedroom. "Move over," she said. "I saw something that scared me and I'm coming into bed with you." The next morning at breakfast she told her family what had happened, but no one else had noticed anything. Her experience remains a puzzle.
Did Dr. Moorman encounter a new type of UAP? Did she imagine the object? Or did she witness a tiny UFO that had come visiting that night?
CATEGORY 2: IDENTIFIED FLYING OBJECTS
Identified flying objects (IFOs) are normal objects that people mistake for something very strange. Many people have gazed at the night sky and sworn that they saw a brightly lit UFO, only to discover that it was actually the planet Venus. In one mass sighting, on New Year's Eve 1978, hundreds of people saw an object in the skies over Western Europe. Some said they saw a long tube like a railroad car; others described a glowing ball of light streaking across the sky. Many believed the object was a solid metallic shape with windows. Despite what people thought, what they actually saw was the re-entry of a booster rocket from a Russian satellite that had been launched a few days earlier. An interesting feature of this IFO sighting, according to UFOlogist Jenny Randles, was that many of the observers refused to believe the official explanation. They believed that they had seen a UFO, no matter what the facts were.
Writer Allen Hendry, who has studied many UFO sightings, discovered that most UFOs turn into IFOs when investigated. One of the cases Hendry investigated occurred in Chicago, Illinois. About 2:30 one night, a man watched through his apartment window as a UFO landed on a grassy area next to Lake Shore Drive (a major highway). The UFO then sat there next to two Chicago Police Department squad cars for two and one-half hours before departing. Hendry doubted that the object was a UFO, and telephoned the Chicago police to ask a few questions. He quickly learned that the place where the UFO had landed also happened to be the landing site for the helicopter used by the police in the 18th District.
In another case, William Athol was driving home about five o'clock one morning near Phillipstown, Massachusetts, when he was blinded by an intense white light in the sky, as if a bomb had exploded. Immediately, his car lost power for a few minutes. Then he saw an object shaped like an orange quarter-moon in the sky.
"So that's the UFO that caused all this!" he concluded. When investigator Hendry checked the story, he discovered that a power transmitter had exploded that night, causing both the blinding flash and the power loss. And the UFO shaped like a quarter-moon was...simply the moon.
CATEGORY 3: TRUE UFOs
Real unidentified flying objects are sometimes called TRUFOs (as in True UFOs). These cannot be explained away as atmospheric phenomena or IFOs. They are what most people think of when they hear the term "UFO": flying saucers and aliens. However, there can be other explanations for TRUFOs, as you will see.
One of the most interesting and well-studied encounters took place over Mansfield, Ohio, Captain Lawrence J. Coyne was the pilot of the crew of an Army Reserve helicopter that left Columbus on evening of October 18 on a flight to the home bas Cleveland. The sky was clear but moonless that night and visibility was approximately fifteen miles.
Near Mansfield the crew noticed a strange red light, Sergeant John Healy saw it first, to the west, but it seemed to be moving away, so he said nothing. About three minutes later, Sergeant Robert Yanacsek saw a small red light to the east, where it appeared to be moving along with the helicopter. Then the light began to move toward the copter.
Fearing that they were about to collide, Captain Coyne thrust the control stick down, and the helicopter began a quick descent. At the same time he requested information from the Mansfield control tower on jet aircraft in the vicinity. However, radio contact was lost, and the helicopter's compass began to spin out of control.
The red light continued to close in, even though the helicopter was in a rapid descent. Suddenly the light began to hover in front of and slightly above it. Coyne, Healy, and Yanacsek each later reported that he saw a cigar-shaped gray metallic object, which filled the entire front windscreen of the helicopter. This object had a red light in front and a white light at the tail. But its most interesting feature was the green beam that came from its lower portion. Without warning, the beam rose up and flooded the helicopter's cockpit with green light.
After a few seconds, the object sped away to the west. As the crew watched the white taillight recede, each man noted that the object made a sharp forty-five degree course change, something impossible in present-day aircraft.
Most amazing of all, even though the helicopter had been in a steep descent, Captain Coyne noticed that was now higher than its original altitude and still climbing. He tried to regain control of it. In a moment he felt a bump, and he began a slow descent to the cruising altitude of 2,500 feet. Coyne was convinced that something had caused the helicopter to rise quickly, even though the control stick was thrust down. That something, he was certain, was a TRUFO.
When UFOlogist Jennie Zeidman became involved in the case, she spent many hours interviewing the helicopter crew and also tried to find witnesses to the sighting on the round. Her persistence paid off when, fifteen years later, she located a family who claimed to have personal knowledge of Captain Coyne's experience.
The Elias family lived below the general flight path to the Mansfield airport and directly beneath the route of the helicopter's flight that night. Although they did not actually see the UFO, Mrs. Jeanne Elias and her fourteen-year-old son John did hear the helicopter. The sound was so loud that Mrs. Elias, who had just gone to bed, thought the craft was going to crash and instinctively stuck her head under the pillow. Later, she laughed with embarrassment as she told Zeidman how foolishly she had reacted.
The sound wakened John, but his reaction was different.
He thought, "Wow, a helicopter is hovering over the house."
Then he watched as a mysterious green light illuminated his bedroom momentarily. John told Zeidman that the green light shone long enough "to make me realize that there was something above the house ... shining a light down on the ground, or around the house, because it was coming in so heavy in my room."
Some skeptics thought that a meteor caused the helicopter's strange encounter. But as UFOlogist Zeidman concluded, the fact that the incident lasted for a long time and involved a green beam of light proved that a meteor was not its cause.
Copyright © James M. Deem. Taken from How to Catch a Flying Saucer (Houghton Mifflin, 1991). All rights reserved.
Other UFO Stories by James M Deem
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CloEncse ounters of the First, Second, and Third Kind Close Encounters of the Fourth Kind
The What's What of UFOs: The Five Most Common Shapes The Who's Who of UFOs: What Their Occupants Look Like
UFO Missions: What UFOs Have Been Seen Doing Tips for Having a Close Encounter