Theories are pouring in to explain what some say was a UFO sighting off P.E.I.'s North Shore in June 2014, but a national UFO group is standing by its conclusion.

Moncton's John Sheppard shot around eight minutes of video showing bright lights in the sky over the Gulf of St. Lawrence while camping at Twin Shores campground in the late spring that year.

He submitted  the video to Mutual UFO Network of Canada (MUFON), which looked into the sighting and concluded it was an unidentified aerial vehicle — or UAV. ​

But a number of people have written to CBC News looking to debunk that conclusion.

Paul Gray, the Halifax president of the Royal Astronomical Society of Canada, has been an amateur astronomer for 27 years, and says he's debunked many alleged UFO sightings.

Gray believes what Sheppard filmed that night was likely the 11:42 p.m. Air Canada flight approaching the Îles-de-la-Madeleine airport. Gray said the airport's main runway is directly in line with the area of the North Shore where Sheppard was filming.

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Another theory is that the lights could have been parachute flares dropped by planes doing search-and-rescue or regular training. (Sunnie Huang/CBC)

He said the landing lights of the aircraft are turned on 10 to 15 minutes before landing and can be seen up to 160 km away, making it possible for someone on the P.E.I. shore to spot them.

As for the erratic behaviour of the light, Gray has a challenge for those who believe this is a UFO.

"Next clear night, if you are 10 to 20 miles from an airport, go out with your cell phone and try to hold it steady for five minutes or more and take a video of the plane on approach. I bet you will find it looks almost the same, a bright light bouncing around the screen," Gray wrote to CBC News. 

He argues MUFON should choose the most likely hypothesis.

"Is it more likely to be a UFO with aliens, or a plane approaching a known runway at night at a known time of arrival?" wrote Gray. 

UFO group stand by conclusion 

But MUFON Canada assistant director Stu Bundy isn't convinced.

He said MUFON's B.C. director is also an astronomer and a former pilot, and he didn't think it was an aircraft on approach.

Bundy said their investigator checked flight schedules out of the Charlottetown and Halifax airports for that night. 

"We could be wrong. Never say never," said Bundy, but he stands by MUFON's conclusion. 

Theories abound

Hugh McCormack, who worked at the P.E.I. National Park in the mid-80s, believes what Sheppard filmed was two parachute flares dropped by Canadian military planes, which he's seen during search-and-rescue exercises or regular training.

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A nearby cottage owner also thought he saw a UFO in the summer of 2014 but it turned out to be a drone owned by another cottage renter. (Associated Press)

Sheppard, in his video, does mention he heard planes a short time before the lights appeared, and in his follow-up interview with CBC News he said a large military plane did make several passes over the campsite the next day. 

Bundy said MUFON is happy to sift through all theories, but he warns that this is a very polarizing subject with many on both sides who believe they know the truth. 

'It flew very similarly to the man's video'

Thunder Cove cottage owner Ross Thompson floated a third theory.

Thompson wrote to CBC News that in the summer of 2014 he thought he saw a UFO between his cottage and the water late one night. But after some investigation, it turned out to be a large drone with multi-coloured lights owned by a cottage renter in the area. 

"It had red, blue and white lights, plus one bright light. It flew very similarly to the man's video," said Thompson. "Moved up and down very quickly and around the area several hundred meters up."

Bundy said MUFON already considered that possibility.

He said one of the group's field investigators in Montreal, who owns a drone company, doubts the lights were caused by one of these flying devices.

"He sells these things and he's very familiar with them and he said it didn't really have any characteristics, or not many, of a drone," said Bundy.