In a series of memos dated all the way to the late 1940s, top CIA officials detail their mounting concern over extraterrestrial life descending upon us. One strange trend quickly emerged to those officials, and one that has remained constant in the 67 years since. Today, as they did in 1949, UFO sightings spike in the summer.

There are several theories about why this happens.

A CIA memo from 1949 captures the agency’s growing concern over UFO activity. CIA

Cassidy Nicholas is the chief archivist for the Mutual UFO Network, or MUFON, an organization started in 1969 that looks into reported UFO sightings. She is perhaps the foremost expert on UFO sightings data, having handled thousands of investigations within the last several years.

Nicholas passed the MUFON data along to Tech Insider, which include sightings since 1960.Skye Gould/Tech Insider

The trend is hard to notice at first, mostly because there only a few dozen reports each month for most of the 20th century. But between May and August the numbers do tend to climb.

It’s a trend that has gotten even easier to spot within the last decade, as more people have heard of MUFON and reported their UFO sightings.

Skye Gould/Tech Insider

Nicholas’ go-to explanation for this summer spike is pretty straightforward.

“[People] are noticing the weather, hiking, camping, doing outside activities,” she tells Tech Insider. “And there seems to be an increase in live events” like concerts, fireworks, and other community gatherings.

In other words, people are simply outside more in the summer, rather than hunched over their phones.

Other possible reasons include blockbuster movies and UFO-related TV shows released during the summer months. This could prime people to label a radio tower or a remote-controlled drone a UFO.

“It’s likely that the media and [alien-themed] movies that are coming out, like Apollo 18 and Paul, are piquing people’s interest in UFOs,” Clifford Clift, the international director of MUFON, told “Life’s Little Mysteries” in 2011.

Given how long the trend has persisted, however, it’s more likely that being outside is the primary reason for reporting.

A third explanation, of course, is that there are indeed more flying saucers in the sky between June and September, although MUFON has yet to confirm that is the case.

Source: Business Insider