Retired NASA astronaut Scott Kelly describes his UFO experience. 'It turns out it was Bart Simpson, a balloon.'

• Retired NASA astronaut Scott Kelly spent over 8,100 consecutive hours in space.
• He said on Wednesday at a NASA meeting that he saw a lot of odd behavior while he was up there.
• But his UFO experience actually happened on Earth while he was flying off Virginia Beach.

UFOs rev up our imaginations and make us dare to wonder about highly-intelligent life beyond Earth. But retired astronaut Scott Kelly is here to tell us that many UFO sightings are probably just our eyes playing tricks on us.

Kelly was part of a panel that convened on Wednesday at NASA headquarters to discuss UFOs, what NASA now refers to as unidentified aerial phenomenon. He described a time when he was flying and his radar intercept office (RIO) thought he spotted a UFO.

"I remember one time I was flying in the warning areas off of Virginia Beach military operating area and my RIO — the guy who sits in the back of the Tomcat — was convinced we flew by a UFO," Kelly said. "So I didn't see it. We turned around. We went to go look at it. It turns out it was Bart Simpson — a balloon."

In 2016, Kelly broke the record for the longest consecutive days (340) spent in space. His record has since been surpassed by NASA astronaut Mark Vande Hei, who reached 353 days on the International Space Station.

Recalling the thousands of hours he spent in space, Kelly said on Wednesday, "Oftentimes, in space, I would see things and I was like, 'That's really not behaving like it should.' And every single time when I would look at it long enough, I would realize that it was atmospheric lensing."

Atmospheric lensing can create optical illusions, like making the sun appear higher in the sky than it actually is. This can actually extend daylight by five minutes along the equator, per NASA.

Optical illusions like this are the result of how the particles in Earth's atmosphere bend and manipulate light, which can make us see distorted versions of reality.

"It was the fact that what I was looking at was actually flying behind the atmosphere and because of the variations in the atmosphere it made the trajectory look like it wasn't going in a straight line," Kelly said.

NASA's meeting on Wednesday was more a call to action for better data collection than it was a revelation for folks looking for answers to UFO conspiracy theories. So are UFOs real, or are they just a trick of the eye?

"We have a community of people who are completely convinced of the existence of UFOs, and we have a community of people who think addressing this question is ridiculous," said David Spergel, the panel's chair. "And I think as scientists, the way to approach questions is you start by saying, 'We don't know,' and then you collect data and you try to calibrate your data well."

Watch Kelly talk more about optical illusions in space in the video below: