On Jan. 14 of last year, an Air Canada pilot flying from Toronto to Zurich, Switzerland, woke up from a nap to see an alarming sight out the cockpit window: what appeared to be a flying object (presumably another plane) flying directly at him. The first officer alerted the pilot, who correctly identified the light and told him not to worry about it, but the first officer almost immediately saw a second set of lights and took evasive action, sending the jet into a steep, sudden dive that injured 16 people and almost resulted in a midair collision with another aircraft flying 1,000 feet lower.

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It was a terrifying, bizarre event over the Atlantic Ocean, but what makes it even stranger is that, according to a new report from the Transportation Safety Board of Canada, the initial light that first officer saw was an optical illusion. He thought it was a UFO — quite literally, an unidentified object flying at the plane. Yet there was no aircraft, identified or otherwise: he had instead seen reflected sunlight from the planet Venus. (The second set of lights—the ones that caused the evasive action—were actually from another aircraft the pilot mistakenly believed was on a collision course with the Air Canada flight.)

Depending on when you measure it (since everything in the universe is in constant motion), Venus is between about 25 million and 162 million miles away. Yet the pilot thought that it was close enough to pose an imminent threat of collision. How could the pilot's estimate of the light's distance to the plane be off by at least 25 million miles? How could an experienced airline pilot mistake a planet for a plane?

It's actually not that difficult to understand and has implications for other UFO sightings.

As this incident shows, accurately judging the size, speed and distance of unknown lights in the night sky is virtually impossible.

A light in the sky might be small and 100 yards away, medium-sized and a few miles away, or even planet-sized and tens of millions of miles away — and there is no way to know the difference. John Nance, a former commercial pilot and ABC News aviation analyst, said that such a mistake, while seemingly inexplicable to the average person, was "not outlandish … a bright light, which can be a planet like Venus, can be very startling, and you can mistake it for an airplane."

Venus and UFOs

The strange fact is that Venus has been responsible for many UFO sightings over the years. This skeptical explanation causes discomfort for many UFO believers, who claim that eyewitness UFO reports by pilots are the most reliable in the world. After all, they claim, experienced pilots are familiar with normal lights in the night sky — surely no pilot could possibly mistake a planet for a nearby flying object!

Robert Sheaffer, a columnist for Skeptical Inquirer magazine and veteran UFO investigator, told Discovery News that "there is a long history of Venus (or some other bright planet or star) being perceived as something that it isn't. Even the UFO proponent Jacques Vallee wrote back in 1966 that "no single object has been misinterpreted as a 'flying saucer' more often than the planet Venus."

In fact, Sheaffer noted, "During World War II, B-29 crews making night bombing raids in Japan reported being followed by a 'ball of fire' that turned out to be Venus. Since then, numerous police officers and pilots have made the same mistake, as did Jimmy Carter, who reported seeing a UFO back in 1969 that turned out to be in exactly the same place as Venus."

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This case came to light primarily because the Air Canada pilot's reaction caused injuries to the passengers (several were hospitalized). While it's impossible to know exactly how often pilots and others mistake Venus (or other ordinary lights in the night sky) for UFOs, it's likely to be underestimated and underreported.

Pilots may be reluctant or embarrassed to admit they mistook a planet for a plane and not report the error (in fact Air Canada initially claimed that the incident was the result of "severe turbulence").

Though this size/distance miscalculation effect is strongest at night, the phenomenon also occurs in daylight when unknown objects are sighted (or recorded) in the sky at an unknown distance from the camera. Whether night or day, without some way of establishing the scale or distance of a flying object, it is impossible to determine its size or speed accurately. (In one recently released UFO video taken at an Air Force base in Chile, it seems that insects — probably bees — were captured in the foreground on videocameras and mistaken for high-speed extraterrestrial spacecraft in the skies.)

Of course Venus does not explain all UFO sightings. But this case proves that even experienced pilots can (and do) mistake our neighboring planet for unexplained lights in the sky.