The most infamous mass triangle UFO sighting was the Phoenix Lights incident of March 13 1997 over Arizona.
Five lights were seen in a formation by thousands of people over three hours from 7.30pm to 10.30pm.
The sightings took place a cross a 300-mile area from Phoenix to Tucson.
It was blamed by officials as military flares at the time.
Another mysterious case was the Belgian UFO wave from November 1989.
Thirty different groups of witnesses, and three groups of police officers, reported seeing on November 29 a large object flying at low altitude.
The craft was described as "flat, of triangular shape, with lights underneath", and being silent as it slowly moved across Belgium towards the Netherlands and Germany.
Just a day before the Gainesville sighting, a band about to go on stage in Torrance, California, reported seeing another triangle UFO at midnight.
A brief report to MUFON said: "Four of us were outside waiting to go onstage and one of us noticed this object in the sky above Palos Verdes and it looked like the Star Trek logo with lights making a boomerang shape, with the lights dimming, and brightening.
"It drifted away and hovered with no noise at all and after 10 minutes or so, it slowly turned position, and drifted out of view."
MUFON is getting an unprecedented amount of reports of the mysterious UFOs, usually from within the US.
Some alien hunters believe they are the motherships of extraterrestrials visiting Earth.
However, many conspiracy theorists believe they are actually secret aircrafts developed by the US Air Force (USAF) which are being tested.
The allegations are that these crafts are created at top-secret military bases like Area 51 in Nevada, by reverse engineering alien technology.
Another low-flying triangle sighting took place on December 2 at 6.50pm in Reno, Nevada.
A witness and two children saw the object from their driveway.
The dad said in his report to MUFON: “My son was looking up at the sky and said,‘Hey guys, look up. Do you see that?’
“He pointed it out as it was directly above us.
"My son said he thought it was an airplane or he was just hallucinating, but after we all saw it we knew it was something else because it made no noise whatsoever and was shaped nothing like an airplane.”
The size of the silent craft was estimated to be between 100 and 300 feet.
He continued: “It was moving in a pretty straight line towards the northwest and the Sierra mountains.
"The thing itself made no noise at all and appeared to be going moderately fast.
"The object itself was shaped almost exactly like the ‘Phoenix Lights’ in Arizona.
"It was very triangular; two edges came together and had lights going up the edges.
Nevada MUFON Assistant State Director Sandra Countiss investigated the case and also closed it as "unknown".
MUFON
A CGI sketcj done by the witness to the triangle sighting in New MIlford, Connecticut.
Another triangle which reportedly flew at about 500 feet was reported to MUFON in November.
The silent, triangle-shaped UFO that made a 90-degree turn was seen in New Milford, Connecticut at 8.45 pm on November 17.
The witness report said: "Approached a stop sign in rural area and noted a brightly lit craft flying very slowly directly towards me at low altitude.
“The white spotlights were very bright and spaced widely apart, making a helicopter unlikely, so I stopped at the intersection to observe what seemed like a strange phenomenon.
"It was so slow, low and silent.
“Moments before it would have been overhead, it made a perfect 90-degree turn.
"At that point I could see its underbelly clearly.
"It was a perfect black triangle, slightly wider at the back than the sides with white and red line of lights along the back flashing in a sequence back and forth."
Connecticut MUFON Field Investigator Warren Fentress is investigating.
Mr Marsh said: "Please remember that most UFO sightings can be explained as something natural or man-made."
Scott Brando runs website ufoofinterest.org which exposes hoax UFO sightings.
He is sceptical any unexplainable sightings have been made.
He says the Phoenix Lights Incident was explained as aircraft and military flares.
He told Express.co.uk: “The Phoenix lights were explained with two different events. The first was the flight of five planes in V-shape formation.
"This is what the witness saw in that day.
"The second event was the launch of military flares over Estrella mountains."
He said of the Belgian UFO Wave: "The Belgian UFO wave began as a normal sighting (some lights in the sky) and then spread virally, but it took more time because at that time the
media coverage had no internet like now."
Referring to triangle UFOs generally, he added: “About other similar sightings I'd like to see some reports by MUFON, however many formation of sky lanterns or the launch of skydivers
Golden Knights were often mistaken for UFOs.”
