Government officials believe that foreign powers and weather balloons are to blame for the recent incidents of unidentified aerial phenomenon.

The Pentagon and intelligence agencies have been stumped for years by the reports of aliens in the sky. Many of the incidents have more mundane explanations.

Intelligence agencies will give a classified document to Congress on Monday, updating a report that said nearly all of the incidents remain unexplained. Some of the incidents that were reported were mostly American military personnel.

Interviews with American officials familiar with the findings of the Pentagon and intelligence agencies were used in the article. The officials were speaking on the condition of anonymity.

Some of the incidents are thought to be connected to Beijing, thanks to the use of drones. American officials say that China wants to learn more about how the US trains its military pilots.

Information about the unexplained phenomena is classified. Pentagon officials keep most of the work secret because they don't want China or other countries to know that the American military spied on them.

Conspiracy theories about government lies are allowed to flourish because of official secrecy.

The Pentagon is committed to principles of openness but must balance that with its obligation to protect sensitive information, sources and methods.

The Pentagon will not rush to conclusions in our analysis.

She said that they were collecting as much data as they could and would share their findings whenever possible.

It was not known how much of the report would be public. Most of the cases that have been resolved have been found to be junk in the sky. Ordinary explanations have been given to the incidents that have been recorded in the past year.

Many of the older incidents are still unexplained and there is not enough data to make a conclusion.

In many cases, observed phenomena are classified as unidentifiable because sensors were not able to collect enough information. We want to make sure we have enough data for our analysis.

The videos do not show space aliens according to other officials.

Ordinary objects, like drones or balloons, have appeared to be strange or frightening due to optical illusions and classified sensors.

The Pentagon said in May that images of green triangles that looked like alien ships were actually drones.

Military officials wouldn't say where or when the images were taken. They think the incidents are examples of attempts to conduct espionage.

The U.F.O. has long believed that many of the videos and pictures of naval aviators appear to be optical illusions that make ordinary objects appear to move faster than possible.

The same conclusion has been reached by military officials.

The other recordings released by the Pentagon have not been categorized as a "surveillance incident" at this time. Pentagon officials don't think that any of them are aliens.

One of the videos shows an object moving quickly. That is an illusion created by the angle of observation, according to an analysis by the military. The object is moving at a rate of 30 miles per hour.

A video called Gimbal shows an object that appears to spin. Military officials believe that the optical design of the classified image sensor makes it appear as if the object is moving in a weird way.

Military analysts are still confused by the third video. The object that was captured in the 2004 video appears to be hovering over the water, jumping erratically, and then peeling away. Military officials say it's hard to explain, but they think it's not alien technology.

Efforts to stamp out alien theories have largely failed. The Pentagon formed groups inside the department to improve data collection and give better explanations.

Military officials have said many times that there is no evidence that any of the images show space alien visitors. Pentagon officials testified in May that the government didn't collect materials from alien landings. The testimony didn't deter enthusiasm for theories about aliens.

Military and intelligence officials have been reluctant to offer alternative theories because they don't have complete information or because they don't want to reveal what they know.

U.F.O. enthusiasts have been able to argue that the government doesn't know what the incidents are because they haven't explained them.

Speculation over conspiracy theories has been used by the U.S. government to prevent secrets from being made public. The government allowed rumors about U.F.O. locations to help hide the development of spy planes.

The use of conspiracy theories as cover for classified programs sows distrust in the American government.

There are some American officials who believe that the Chinese government's secret monitoring of military bases could lead to conspiracy theories and make people distrust the government even more.

ImageScott Bray, the deputy director of Navy intelligence, briefing the House Intelligence Committee in May.
Scott Bray, the deputy director of Navy intelligence, briefing the House Intelligence Committee in May.Credit...Michael A. McCoy for The New York Times
Scott Bray, the deputy director of Navy intelligence, briefing the House Intelligence Committee in May.

The Pentagon declassified the conclusions about two images of green triangles recorded in two separate incidents, one on the East Coast and the other on the West. The green triangles were actually drones with a trick of the camera lens and night vision technology turning them into glowing triangles that look like alien spaceships.

Scott W. Bray is the deputy director of naval intelligence.

Mr Bray explained why the government wasn't releasing more information.

Mr. Bray doesn't want potential adversaries to know how we come to a conclusion. It is necessary to consider disclosures on a case-by-case basis.