WASHINGTON -- They are big, fly in the dark, and look otherworldly.

For years, people have reported black triangle-shaped craft floating through nighttime skies. These vehicles are claimed by some as proof that Earth is a tourist off-ramp for visitors from afar. But a more terrestrial, less cosmic, modus operandi may be at work.

New data collected by a group studying purported unidentified flying objects (UFO) is peeling away mystery to find a pattern.

And if you think the skies are full of wild, weird and wondrous things now, wait a few years.

For the last several years, the National Institute for Discovery Science (NIDS), based in Las Vegas, Nevada, has been amassing both historical and recent eyewitness accounts of "triangular" object sightings.

Kelleher said that NIDS has compared its research with triangular/deltoid craft sightings recorded by the Mutual UFO Network (MUFON) and those of investigator Larry Hatch, who currently manages one of the largest UFO databases in the world.

Taking the three independent UFO data sets, NIDS plotted the sighting locations on maps of the United States.

Kelleher said that a lot of the sightings appeared to fall into a broad trend.

Sightings of the triangular objects could be clustered and correlated with a small subset of United States Air Force bases. That subset can be tied to air corridors between Air Force Materiel Command (AFMC) and Air Mobility Command (AMC) bases around the country.

For instance, Wright-Patterson Air Force Base, Headquarters AFMC in Dayton, Ohio seems to be a focal point. Scott Air Force Base, Headquarters AMC, near O'Fallon, Illinois runs a close second.

The fact that, specifically, AFMC or AMC bases appear to be associated with hundreds of triangular object sightings has led NIDS experts to speculate that these "unacknowledged aircraft" are large troop or material carriers.

A vast majority of the triangular-shaped vehicles have been seen only after dark, Kelleher said.

"We are encouraging more people to call in their observations. Right now, what we have is an apparent correlation. People living close to some of these bases can help us close the loop, reporting objects either taking off or landing. That's data we don't have," he said.

The hope of NIDS is to move the unidentified triangular objects into the identified flying object (IFO) realm.

"These objects are being lumped in with the UFO category," Kelleher said. "If we can definitely, to our satisfaction, show a lot of evidence that these are unacknowledged aircraft from the U.S. military and that they fly between these bases, then we don't have to spend a huge amount of time on that.

"Then we can transfer 20 percent of our database from the UFO to the IFO category. That's a fairly big jump," Kelleher said. "We're not a hobby club looking into exotic aircraft. We're investigating the UFO phenomenon."

In June, NIDS announced that newly printed Federal Aviation Administration (FAA) manuals have cited the research group as the sole contact point in the United States to which the FAA reports UFOs.