The Scientific Reason Planes Sometimes Look Like They're Frozen Midair

You've probably seen the viral videos where planes appear to be frozen in the sky, hovering in place rather than flying forward as they usually do. While some are quick to call the situation a glitch in the matrix, there's a fairly simple explanation: It's an optical illusion due to the parallax effect. 

In other words, the planes aren't actually stuck in midair. Our eyes (and brains) are playing tricks on us because we, as the viewers, are moving at a different speed or in a different direction than the plane. As such, we perceive the plane as being frozen, even though it's still moving forward. Here's how the parallax effect works.

How the Parallax Effect Works

"Parallax is the difference that we see in the position of nearby objects relative to background objects because of a changing point of view," Jason Steffen, an associate professor of physics at the University of Nevada, Las Vegas, tells Travel + Leisure. So, when an observer moves, the position of an object in front of them appears to change, even if that object is static. 

In fact, you can experience parallax right now, wherever you are, without moving from the spot you're in. Hold your arm out straight, directly in front of you, and put a finger up in the air. Look at your finger with both eyes open, then switch between looking at your finger with just your right eye and just your left eye. You'll notice that your finger appears to move back and forth. 

That's because your eyes are in different positions on your face, so each eye sees your finger from a slightly different perspective. Our brain automatically interprets the discrepancy (or parallax) as depth. "Without the difference in the images between your left and right eye, which is parallax, you could not have any depth perception," says Steffen.

Motion parallax happens when you're looking out the window of a moving car — objects closer to you appear to whiz by, while objects farther away appear still or very slow-moving. And that's directly related to what's happening in the videos of the frozen planes.

Related: How Many Planes Are in the Air Right Now?

How the Parallax Effect Makes Planes Look Like They’re Floating

There's one common thread between each video of a plane "hovering" in the air: The person recording the video is in a moving vehicle, whether that's another aircraft or a car. And this is key to the optical illusion.

"If you are moving as you film, you will see the airplane's position relative to the background," says Steffen. "If the motion of the video camera keeps the airplane in line with a background object, you won't see the airplane move across the field of view."

This can be seen in videos taken from planes flying parallel to one another. This happens frequently when landing at certain airports with parallel runways, such as San Francisco International Airport (SFO). Not all planes land at the same exact speed, so it's easy for one to move ahead of its neighbor. And from the perspective of the faster plane, it may look like the slower one is frozen in place. "It's like when you pass someone on the freeway, and they look like they are moving backward, when in fact they are moving forward," says Steffen.

In some of the videos — notably the ones taken from cars — there aren't any background objects at all. Instead, there's nothing but sky behind the planes. In that scenario, your brain lacks reference points for accurate depth perception, and it can easily be tricked into perceiving the plane as motionless.

In either case, the optical illusion will disappear if the viewer simply stops moving. Then you'll see the plane moving forward normally.

Related: 25 Things You Should Do Before Boarding a Plane, According to a Frequent Flier

How Astronomers Use Parallax for Research

Parallax isn't only an optical illusion that makes planes look like they're hovering — or a tool your brain uses for depth perception in everyday life. Astronomers use parallax to determine the distance of stars.

"For astronomy, parallax usually refers to observations of nearby stars relative to background stars at different points along the Earth's orbit around the sun," says Steffen. "Parallax is crucial for establishing the 'distance ladder,' which is how we measure distances to different astronomical objects."

Astronomers have to wait quite some time between observations in order to observe parallax between celestial bodies — they can't simply close one eye at a time or drive down a highway to perceive a shift. Instead, they make one observation and then wait six months for the Earth to be on the opposite side of its orbit. That's a distance of approximately 186 million miles (300,000 kilometers), per Astronomy.com, which is enough to observe the parallax effect in distant stars.