You didn’t see a UFO. It was probably one of these things.

UFOs were, for decades, the stuff of science fiction and conspiracy theory circles. But the highest levels of the US government have started seriously considering these phenomena—redubbing them Unidentified Anomalous Phenomena, or UAPs. There have been hearings on Capitol Hill, Pentagon reports, and a NASA working group, all looking into more than 100 currently unexplained UAP sightings, often made by military pilots who caught something unfathomable on their sensors. And plenty of civilians see things they don’t know how to explain, either.

Even if UAPs have gone mainstream, the vast majority of human sightings turn out to be perfectly explicable, though occasionally rare, phenomena. And Jonathan McDowell, an astrophysicist at the Center for Astrophysics | Harvard & Smithsonian, hears about them all.

“I get a lot of social media questions and emails, and occasionally cold calls from random people who have seen something weird in the sky,” McDowell says. Around 90 percent of the conversations, he says, go something like this: ‘Is this space debris, Jonathan?’ No, it’s just a meteor, because it blew up in only two seconds. Or: ‘Is this a UFO?’ No, it’s a Falcon 9 [rocket] launch. ‘Is this aliens?’ Well, that depends on where you think Elon comes from.”

But it’s rarely ignorance or credulity that leads people to mistake a rocket launch or an aircraft for a UAP. Instead, it’s just how human perception works.

“Our ability to estimate how far away something is sucks when it’s not in a context where we have the usual clues,” McDowell says. A close-by insect moving in a peculiar way might be confused for something much farther. Or a shining light might appear close—when it’s actually Venus, 35 million miles or so away.

popsci.com